The role of amino acid side chains in stabilizing dipeptides: the laser ablation Fourier transform microwave spectrum of Ac-Val-NH2. Issue 36 (6th September 2017)

• Record Type: Journal Article
• Authors: León, I.; Alonso, E. R.; Mata, S.; Cabezas, C.; Rodríguez, M. A.; Grabow, J.-U.; Alonso, J. L.
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 36(2017)
• Page Start: 24985
• Page End: 24990
• Publication Date: 2017-09-06
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp03924g
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The steric effects imposed by the isopropyl group of valine in the conformational stabilization of the capped dipeptide N -acetyl-l -valinamide (Ac-Val-NH2 ) have been studied by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy. Abstract : The steric effects imposed by the isopropyl group of valine in the conformational stabilization of the capped dipeptide N -acetyl-l -valinamide (Ac-Val-NH2 ) have been studied by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy. The rotational and quadrupole coupling constants of the two 14 N nuclei determined in this work show that this dipeptide exists as a mixture of C7 and C5 conformers in the supersonic expansion. The conformers are stabilized by a CO⋯H–N intramolecular hydrogen bond closing a seven- or a five-membered ring, respectively. The observation of both conformers is in good agreement with previous results on the related dipeptides containing different residues, confirming that the polarity/non-polarity of the side chains of the amino acid is responsible for the conformational locking/unlocking. The voluminous isopropyl group is not able to prevent the less stable C5 conformer from forming but it destabilizes the CO⋯H–N interaction.