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Abstract:
Infrared/UV hole-burning spectroscopy is performed on individual conformers of the protected dipeptide Z-Aib-Pro-NHMe. The extended IR range probed in this study allows one to elucidate both the H-bonding motif (5-7 μm) as well as the backbone structure (7-10 μm). Comparison with DFT calculations shows that the backbone is locally constrained to an α-conformation by Aib and to a γ-turn by Pro. The γ-turn motif observed here is intriguing since the condensed phase structure is known to be a β-turn. This is the first actual observation of such a discrepancy, and it emphasizes the subtle balance between intra- and intermolecular forces, which is responsible for the relative stability of the different secondary structure motifs.
