Tyrosine-glycine revisited : resolving the discrepancy between theory and experiment

Abstract

Energies of 20 conformers of the Tyr-Gly dipeptide were computed using DSD-PBEP86-D3BJ/aug-cc-VTZ, with geometries from M06-2X/6-31+G* and B97-D/6-31+G*. At 0 K, these energies support the earlier finding from MP2/6-31+G*//B3LYP/6-31+G*, that the most stable conformer is folded and H-bonded. However, when free-energy corrections at 400 K are added, non-H-bonded conformers are the most stable. This supports an earlier spectroscopic study in which H-bonded conformers were absent. Of the four most stable conformers at 400 K, two were not matched with spectra in the experimental study, but we argue that all four can in fact be plausibly assigned to the experimental spectra.