Computational modeling of the gas phase Hydrogen/Deuterium (H/D) exchange with D2O of 3 protonated tripeptides containing L-phenylalanine, GGF, GFG and FGG, was carried out to study the effect of the phenyl ring on gas phase peptide structures and H/D exchange kinetics. In gas phase, protonated tripeptides fold into a globular structure with strong hydrogen bond between C- and N-terminus, with cation−π also being a major driving force in the folding process. With the exception of GGF, the most stable conformation does not exchange directly, but rather undergoes significant conformational change upon complexation with D2O, and forms a more reactive structure to exchange. Exchange barrier decreases from FGG, GGF to GFG, agreeing with previously obtained mass spectrometry data that exchange rate increases from FGG, GGF to GFG. For GGF, the presence of the phenyl ring renders direct exchange equally favorable because O-D…π interaction stabilizes transition state and lowers the exchange barrier. Additionally, cation−π between N-terminus and phenyl ring stabilizes the peptide-D2O complex and increases the exchange barrier of FGG. These results provide insights into the role of the phenyl ring in stabilizing peptide conformations.

Gas phase structure and hydrogen/deuterium exchange of protonated tripeptides containing L-phenylalanine

255th National Meeting (2018)

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