Mid-infrared spectroscopy of protected peptides in the gas phase: a probe of the backbone conformation

J Am Chem Soc. 2006 Mar 22;128(11):3592-7. doi: 10.1021/ja055378h.

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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminoisobutyric Acids / chemistry*
  • Dipeptides / chemical synthesis
  • Dipeptides / chemistry*
  • Gases
  • Models, Molecular
  • Proline / chemistry*
  • Protein Structure, Secondary
  • Spectrophotometry, Infrared
  • Spectrophotometry, Ultraviolet
  • Thermodynamics

Substances

  • Aminoisobutyric Acids
  • Dipeptides
  • Gases
  • Proline