Peer-reviewed Publications |
Gutierrez-Quintanilla, A., Chevalier M, Platakyte, R., Ceponkus J, & Crepin, C. (2020). Intramolecular hydrogen tunneling in 2-chloromalonaldehyde trapped in solid para-hydrogen. Phys Chem Chem Phys, 20, 28658–28666.
Résumé: The internal dynamics of a 2-chloromalonaldehyde (2-ClMA) molecule, possessing a strong internal hydrogen bond (IHB), was examined by means of matrix isolation spectroscopy in a soft host: para-hydrogen (pH2). 2-ClMA is a chlorinated derivative of malonaldehyde (MA), a model molecule in hydrogen transfer studies, better suited to low temperature experiments than its parent molecule. The infrared absorption spectra of 2-ClMA isolated in pH2 exhibit temperature dependent structures which are explained as transitions occurring from split vibrational levels induced by hydrogen tunneling. The doublet components associated with higher and lower energy levels are changing reversibly with the increase/decrease of the matrix temperature. The ground state splitting is measured to be 7.9 +/- 0.1 cm(-1). The presence of oH2 impurities in the pH2 matrix close to the neighborhood of the 2-ClMA molecule is found to quench the H tunneling. The data provide a powerful insight into the dynamical picture of intramolecular hydrogen tunneling in a molecule embedded in a very weakly perturbing environment.
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Hartwig, B., Lange, M., Poblotzki, A., Medel, R., Zehnacker, A., & Suhm, M. A. (2020). The reduced cohesion of homoconfigurational 1,2-diols. PCCP, 22(3), 1122–1136.
Résumé: By a combination of linear FTIR and Raman jet spectroscopy, racemic trans-1,2-cyclohexanediol is shown to form an energetically unrivalled S4-symmetric heterochiral dimer in close analogy to 1,2-ethanediol. Analogous experiments with enantiopure trans-1,2-cyclohexanediol reveal the spectral signature of at least three unsymmetric homochiral dimers. A comparison to signal-enhanced spectra of 1,2-ethanediol and to calculations uncovers at least three transiently homochiral dimer contributions as well. In few of these dimer structures, the intramolecular OH⋯O contact present in monomeric 1,2-diols survives, despite the kinetic control in supersonic jet expansions. This provides further insights into the dimerisation mechanism of conformationally semi-flexible molecules in supersonic jets. Racemisation upon dimerisation is shown to be largely quenched under jet cooling conditions, whereas it should be strongly energy-driven at higher temperatures. The pronounced energetic preference for heterochiral aggregation of vicinal diols is also discussed in the context of chirality-induced spin selectivity.
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Hirata, K., Mori, Y., Ishiuchi, S. -ichi, Fujii, M., & Zehnacker, A. (2020). Chiral discrimination between tyrosine and β-cyclodextrin revealed by cryogenic ion trap infrared spectroscopy. PCCP, 22(43), 24887–24894.
Résumé: Complexes of permethylated β-cyclodextrin (β-MCD) with the two enantiomers of protonated tyrosine (l- and d-TyrH+) are studied by cryogenic ion trap infrared photo-dissociation spectroscopy. The vibrational spectra in the OH/NH stretch and fingerprint regions are assigned based on density functional theory calculations. The spectrum of both l- and d-TyrH+ complexes contains features characteristic of a first structure with ammonium and acid groups of the amino acid simultaneously interacting with the β-MCD, the phenolic OH remaining free. A second structure involving additional interaction between the phenolic OH and the β-MCD is observed only for the complex with d-TyrH+. The larger abundance of the d-TyrH+ complex in the mass spectrum is tentatively explained in terms of (1) better insertion of d-TyrH+ within the cavity with the hydrophobic aromatic moiety less exposed to hydrophilic solvent molecules and (2) a stiff structure involving three interaction points, namely the ammonium, the phenolic OH and the carboxylic acid OH, which is not possible for the complex with l-TyrH+. The recognition process does not occur through size effects that induce complementarity to the host molecule but specific interactions. These results provide a comprehensive understanding of how the cyclodextrin recognises a chiral biomolecule.
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Imani, Z., Mundlapati, V. R., Goldsztejn, G., Brenner, V., Gloaguen, E., Guillot, R., Baltaze, J. P., Le Barbu-Debus, K., Robin, S., Zehnacker, A., Mons, M., & Aitken, D. J. (2020). Conformation control through concurrent N–H⋯S and N–H⋯O=C hydrogen bonding and hyperconjugation effects. CHEMICAL SCIENCE, 11(34), 9191–9197.
Résumé: In addition to the classical N-HMIDLINE HORIZONTAL ELLIPSISO-C non-covalent interaction, less conventional types of hydrogen bonding, such as N-HMIDLINE HORIZONTAL ELLIPSISS, may play a key role in determining the molecular structure. In this work, using theoretical calculations in combination with spectroscopic analysis in both gas phase and solution phase, we demonstrate that both these H-bonding modes exist simultaneously in low-energy conformers of capped derivatives of Attc, a thietane alpha-amino acid. 6-Membered ring inter-residue N-HMIDLINE HORIZONTAL ELLIPSISS interactions (C6(gamma)), assisted by hyperconjugation between the thietane ring and the backbone, combine with 5-membered ring intra-residue backbone N-HMIDLINE HORIZONTAL ELLIPSISO-C interactions (C5) to provide a C5-C6(gamma)feature that stabilizes a planar geometry in the monomer unit. Two contiguous C5-C6(gamma)features in the planar dimer implicate an unprecedented three-centre H-bond of the type C-OMIDLINE HORIZONTAL ELLIPSISH(N)MIDLINE HORIZONTAL ELLIPSISSR2, while the trimer adopts two C5-C6(gamma)features separated by a Ramachandran alpha-type backbone configuration. These low-energy conformers are fully characterized in the gas phase and support is presented for their existence in solution state.
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Le Barbu-Debus, K., Bowles, J., Jähnigen, S., Clavaguéra, C., Calvo, F., Vuilleumier, R., & Zehnacker, A. (2020). Assessing cluster models of solvation for the description of vibrational circular dichroism spectra: synergy between static and dynamic approaches. PCCP, 22, 26047–26068.
Résumé: Solvation effects are essential for defining the shape of vibrational circular dichroism (VCD) spectra. Several approaches have been proposed to include them into computational models for calculating VCD signals, in particular those resting on the “cluster-in-a-liquid” model. Here we examine the capabilities of this ansatz on the example of flexible (1S,2S)-trans-1-amino-2-indanol solvated in dimethyl sulfoxide (DMSO). We compare cluster sets obtained from static calculations with results from explicit molecular dynamics (MD) trajectories based on either force field (FF) or first-principles (FP) methods. While the FFMD approach provides a broader sampling of configurational space, FPMD and time-correlation functions of dipole moments account for anharmonicity and entropy effects in the VCD calculation. They provide a means to evaluate the immediate effect of the solvent on the spectrum. This survey singles out several challenges associated with the use of clusters to describe solvation effects in systems showing shallow potential energy surfaces and non-covalent interactions. Static structures of clusters involving a limited number of solvent molecules satisfactorily capture the main effects of solvation in the bulk limit on the VCD spectra, if these structures are correctly weighted. The importance of taking into consideration their fluxionality, i.e. different solvent conformations sharing a same hydrogen bond pattern, and the limitations of small clusters for describing the solvent dynamics are discussed.
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Le Barbu-Debus, K., Scuderi, D., Lepère, V., & Zehnacker, A. (2020). Homochiral vs. heterochiral sodium core dimers of tartaric acid esters: A mass spectrometry and vibrational spectroscopy study. Journal of Molecular Structure, 1205, 127583.
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Pérez-Mellor, A., Le Barbu-Debus, K., & Zehnacker, A. (2020). Solid-state synthesis of cyclo LD-diphenylalanine: A chiral phase built from achiral subunits. Chirality, 32(5), 693–703.
Résumé: Abstract The solid-state structure of LL/DD or LD/DL diphenylalanine diluted in KBr pellets is studied by infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy. The structure depends on the absolute configuration of the residues. The natural LL diphenylalanine exists as a mixture of neutral and zwitterionic structures, depending on the humidity of the sample, while mostly the zwitterion is observed for LD diphenylalanine whatever the experimental conditions. The system undergoes spontaneous cyclization upon heating at 125°C, resulting to the formation of a diketopiperazine (DKP) dipeptide as the only product. The reaction is faster for LD than for LL diphenylalanine. As expected, LL and DD diphenylalanine react to form the LL and DD enantiomers of cyclo diphenylalanine. Interestingly, the DKP dipeptides formed from the LD or DL diphenylalanine show unexpected optical activity, with opposite VCD spectra for the products formed from the LD and DL reagents. This is explained in terms of chirality synchronization between the monomers within the crystal, which retain the symmetry of the reagent, resulting to the formation of a new chiral phase made from transiently chiral molecules.
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Strom, A. I., Gutierrez-Quintanilla A, Chevalier, M., Ceponkus J, Crepin, C., & Anderson DT. (2020). Matrix Isolation Spectroscopy and Nuclear Spin Conversion of Propyne Suspended in Solid Parahydrogen. J Phys Chem A, 124(22), 4471–4483.
Résumé: Parahydrogen (pH2) quantum solids are excellent matrix isolation hosts for studying the rovibrational dynamics and nuclear spin conversion (NSC) kinetics of molecules containing indistinguishable nuclei with nonzero spin. The relatively slow NSC kinetics of propyne (CH3CCH) isolated in solid pH2 is employed as a tool to assign the rovibrational spectrum of propyne in the 600-7000 cm(-1) region. Detailed analyses of a variety of parallel (DeltaK = 0) and perpendicular (DeltaK=+/-1) bands of propyne indicate that the end-over-end rotation of propyne is quenched, but K rotation of the methyl group around the C3 symmetry axis still persists. However, this single-axis K rotation is significantly hindered for propyne trapped in solid pH2 such that the energies of the K rotational states do not obey simple energy-level expressions. The NSC kinetics of propyne follows first-order reversible kinetics with a 287(7) min effective time constant at 1.7 K. Intensity-intensity correlation plots are used to determine the relative line strengths of individual ortho- and para-propyne rovibrational transitions, enabling an independent estimation of the ground vibrational state effective A'' constant of propyne.
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Szczepaniak, U., Gutiérrez-Quintanilla, A., Crépin, C., Guillemin, J. - C., Turowski, M., Custer, T., & Kołos, R. (2020). Spectroscopy of methylcyanodiacetylene revisited. Solid parahydrogen and solid neon matrix studies. Journal of Molecular Structure, 1218, 128437.
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Szczepaniak, U., Ozaki, K., Tanaka, K., Ohnishi, Y., Wada, Y., Guillemin, J. - C., Crépin, C., Kołos, R., Morisawa, Y., Suzuki, H., & Wakabayashi, T. (2020). Phosphorescence excitation mapping and vibrational spectroscopy of HC9N and HC11N cyanopolyynes in organic solvents. Journal of Molecular Structure, 1214, 128201.
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