Speaker
Description
Studies on the structures and conformations of microsolvated peptides in the gas
phase are scarce in the literature. This scarcity arises primarily from the difficulty of
achieving sufficient cooling during jet expansion when laser desorption is used to
vaporize peptides and generate microhydrated peptide clusters. In this work, we
investigate the effect of microhydration on the secondary structure of a capped
dipeptide, Boc-DPro-Gly-NHBn-OMe (Boc = tert-butyloxycarbonyl, Bn = benzyl), i.e.,
Pro–Gly (PG), in the presence of a single H₂O molecule using gas-phase laser
spectroscopy combined with quantum chemical calculations. In the gas phase, the PG
monomer adopts a C7–C7 conformation, whereas in the condensed phase, it assumes
a β-turn structure.1 IR–UV hole-burning spectroscopy of PG⋅⋅⋅(H₂O)₁ confirms the
observation of a single conformer in the experiment. Both experimental and theoretical
IR spectra demonstrate that the H₂O molecule is selectively inserted into the relatively
weak C7 hydrogen bond (γ-turn) formed between the Pro C=O and NHBn N–H groups,
while the other C7 hydrogen bond (γ-turn) between the Gly N–H and Boc C=O groups
remains unaffected. Consequently, the single H₂O molecule in the PG⋅⋅⋅(H₂O)₁
complex significantly distorts the peptide backbone without appreciable alteration of
the overall secondary structural motif (γ–γ) of the isolated PG monomer.2 This study
of the monohydrated peptide suggests that multiple water molecules may be required
to switch the secondary structure of PG from the double γ-turn to the β-turn
conformation that is favored in the condensed phase. Future work is in progress to
study the conformations of PG with a larger number of water molecules.
References
1. S. Kumar, K. Borish, S. Dey, J. Nagesh, and A. Das, Phys. Chem. Chem. Phys.
2022, 24, 18408.
2. S. Mandal, A. Kossov, P. Carcabal, and A. Das, J. Chem. Phys. 2024, 161,
214304.
| This abstract is submitted for.... | HBond 2025 conference |
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