Mid-infrared spectroscopy of protected peptides in the gas phase: a probe of the backbone conformation.
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 microm) as well as the backbone structure (7-10 microm). Comparison with DFT calculations shows that the backbone is locally constrained to an alpha-conformation by Aib and to a gamma-turn by Pro. The gamma-turn motif observed here is intriguing since the condensed phase structure is known to be a beta-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.
FOM Institute for Plasma Physics Rijnhuizen, Edisonbaan 14, NL-3439 MN Nieuwegein, The Netherlands.
Isabelle
I
Compagnon
Jos
J
Oomens
Gerard
G
Meijer
Gert
G
von Helden
D000621:Aminoisobutyric Acids / Q000737:chemistry*; D004151:Dipeptides / Q000138:chemical synthesis / Q000737:chemistry*; D005740:Gases; D008958:Models, Molecular; D011392:Proline / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
D000621:Aminoisobutyric Acids; D004151:Dipeptides; D005740:Gases; D011392:Proline