[XxxProGlyGly + H]+ ions, where Xxx = all 20 naturally occurring amino acids, were formed by electrospray ionization and their collision cross sections were measured by ion mobility spectrometry-mass spectrometry. Most show only a single conformer at 25 °C, but four (Xxx = Gly, His, Lys, Gln) show appreciable amounts of two conformers, believed to correspond to cis and trans conformations of the proline residue. Observation of only one conformer implies that ΔG between the two forms is too large to allow an appreciable population of the higher energy conformer at equilibrium. The four peptides listed above are examined for structural factors that stabilize the higher energy proline conformer such that both forms are observed in the equilibrium distribution.

Survey of proline conformational behavior in protonated gas-phase XxxProGlyGly

253rd National Meeting (2017)

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