The aim of this research is to develop anharmonic calculations of vibrational spectroscopy, combined with experimental data, as a tool for determining the atomistic 3D structures of conformers of isolated peptides. We present results of calculations using Vibrational Self Consistent Field (VSCF) algorithms for several peptides conformers, including NATA, AVPO, Gramicidin S and Gramicidins S (H2O)2. Good agreement with experiment is found for frequencies of hydrogenic stretches , to an extend that supports assigning a 3D structure for individual conformers. Agreement with experiment for peak intensities is satisfactory, but less good, while computations and experiments differ significantly for the spectral lineshapes. Strongly anharmonic peak positions, associated with hydrogenic stretches play a key role in the comparisons with experiments. The state of the art in determining peptide structures by comparing anharmonic calculations with experiment in analyzed in light of the results, and approaches for further progress are outlined.

First-principles anharmonic computational spectroscopy of peptides: Determination of the 3D structures of conformers

251st National Meeting (2016)

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