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Article

Decoding the Structure of Non-Proteinogenic Amino Acids: The Rotational Spectrum of Jet-Cooled Laser-Ablated Thioproline

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Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, IU CINQUIMA Universidad de Valladolid, 47011 Valladolid, Spain
2
Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid, Spain
*
Author to whom correspondence should be addressed.
Current Address: Département de Physique Moléculaire, IPR (Institut de Physique de Rennes), CNRS-UMR 6251, Université de Rennes 1, F-35000 Rennes, France.
Academic Editor: Maria Eugenia Sanz
Molecules 2021, 26(24), 7585; https://doi.org/10.3390/molecules26247585
Received: 16 November 2021 / Revised: 10 December 2021 / Accepted: 12 December 2021 / Published: 14 December 2021
The broadband rotational spectrum of jet-cooled laser-ablated thioproline was recorded. Two conformers of this system were observed and identified with the help of DFT and ab initio computations by comparison of the observed and calculated rotational constants and 14N quadrupole coupling constants as well as the predicted energies compared to the observed relative populations. These conformers showed a mixed bent/twisted arrangement of the five-membered ring similar to that of the related compound thiazolidine with the N–H bond in axial configuration. The most stable form had the COOH group in an equatorial position on the same side of the ring as N-H. The arrangement of the C=O group close to the N-H bond led to a weak interaction between them (classified as type I) characterized by a noncovalent interaction analysis. The second form had a trans-COOH arrangement showing a type II O–H···N hydrogen bond. In thioproline, the stability of conformers of type I and type II was reversed with respect to proline. We show how the conformation of the ring depends on the function associated with the endocyclic N atom when comparing the structures of isolated thioproline with its zwitterion observed in condensed phases and with peptide forms. View Full-Text
Keywords: laser-ablation; rotational spectroscopy; amino acids; computational chemistry; intramolecular interactions laser-ablation; rotational spectroscopy; amino acids; computational chemistry; intramolecular interactions
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MDPI and ACS Style

López, J.C.; Macario, A.; Verde, A.; Pérez-Encabo, A.; Blanco, S. Decoding the Structure of Non-Proteinogenic Amino Acids: The Rotational Spectrum of Jet-Cooled Laser-Ablated Thioproline. Molecules 2021, 26, 7585. https://doi.org/10.3390/molecules26247585

AMA Style

López JC, Macario A, Verde A, Pérez-Encabo A, Blanco S. Decoding the Structure of Non-Proteinogenic Amino Acids: The Rotational Spectrum of Jet-Cooled Laser-Ablated Thioproline. Molecules. 2021; 26(24):7585. https://doi.org/10.3390/molecules26247585

Chicago/Turabian Style

López, Juan Carlos, Alberto Macario, Andrés Verde, Alfonso Pérez-Encabo, and Susana Blanco. 2021. "Decoding the Structure of Non-Proteinogenic Amino Acids: The Rotational Spectrum of Jet-Cooled Laser-Ablated Thioproline" Molecules 26, no. 24: 7585. https://doi.org/10.3390/molecules26247585

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