Probing the γ-Turn in a Short Proline Dipeptide Chain

Authors

  • Dr. Carlos Cabezas,

    1. Grupo de Espectroscopía Molecular (GEM), Unidad Asociada CSIC Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Universidad de Valladolid, 47005 Valladolid (Spain)
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  • Marcelino Varela,

    1. Grupo de Espectroscopía Molecular (GEM), Unidad Asociada CSIC Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Universidad de Valladolid, 47005 Valladolid (Spain)
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  • Prof. José L. Alonso

    Corresponding author
    1. Grupo de Espectroscopía Molecular (GEM), Unidad Asociada CSIC Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Universidad de Valladolid, 47005 Valladolid (Spain)
    • Grupo de Espectroscopía Molecular (GEM), Unidad Asociada CSIC Edificio Quifima, Laboratorios de Espectroscopia y Bioespectroscopia, Parque Científico UVa, Universidad de Valladolid, 47005 Valladolid (Spain)
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Abstract

The small peptide derived from proline, N-acetyl-prolinamide (Ac-Pro-NH2), has been investigated using a combination of Fourier transform microwave spectroscopy with laser ablation. Spectral signatures belonging to only one conformer have been detected in the supersonic expansion. Rotational constants and nuclear quadrupole coupling constants of the two 14N nuclei have been used in the characterization of a γ-turn structure in the gas phase, which is stabilized by a CO⋅⋅⋅HN intramolecular hydrogen bond closing a seven-membered ring. A methyl group internal rotation barrier of 354 cm−1 has been determined from the analysis of the A–E splittings.

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