The structure of the gas-phase tyrosine-glycine-glycine tripeptide

Abstract

The structure of the neutral gas-phase tripeptide Tyr-Gly-Gly has been investigated using different strategies that employ a hierarchy of electronic structure theory (single-point HF/3-21G* energy calculation, HF/3-21G* geometry optimization, B3LYP/6-31+G* geometry optimization and MP2/6-31+G* single-point energy calculation). All 20 most stable conformers according to the single-point MP2 calculations adopt a folded structure. In the most stable structure found the C-terminal carboxylic acid group interacts with both the carboxyl C=O of glycine (2) and the tyrosine OH (forming an OH···O=C-OH···O=C hydrogen-bonding chain), with an additional NH···N interaction involving the NH of glycine (2) and the N-terminal amino group. Harmonic vibrational frequencies (N–H, C–H and C=O stretch frequencies and NH and OH in-plane bending frequencies) are reported to aid future spectroscopic studies on this peptide.

Acknowledgements

We gratefully acknowledge support from the Engineering and Physical Sciences Research Council (through grants GR/R63196/01, GR/S06233/01, and GR/R94466). TvM is grateful for support from the Royal Society under the University Research Fellowship scheme. DT gratefully acknowledges the ChemReact Computer Consortium for a PhD studentship.

Notes

¹ A particular X-H-Y atom group was considered to form an H-bond interaction if R_HY ≤ 2.6 Å, ∠(X-H-Y) ≥ 100°, and Y ≠ (C or H). Interactions with π-electron clouds (R_HY ≤ 2.6 Å where Y is the midpoint of the aromatic ring, ∠(X-H-Y) ≥ 95°) were counted as half.