Is β-homo-proline a pseudo-γ-turn forming element of β-peptides? An IR and VCD spectroscopic study on Ac-β-HPro-NHMe in cryogenic matrices and solutions

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Abstract

In order to test the pseudo-γ-turn forming capability of β-homo-proline (β3-HPro) 2-[(2S)-1-acetylpyrrolidin-2-yl]- N-methylacetamide (Ac-β3-HPro-NHMe) was synthesized and its potential energy landscape was investigated by infrared (IR) and vibrational circular dichroism (VCD) spectroscopy combined with density functional calculations. Based upon a comparison between experimental and computed spectra three different pseudo-γ-turn-like trans conformers and a cis conformer were identified in low-temperature Ar and Kr matrices. The computations in agreement with the observations reveal that, in contrast to its α-Pro analogue, the room-temperature abundance of the cis conformer is significant, falling above 10% in the isolated phase. Furthermore, solution-phase vibrational spectra and computations show that the cis conformer is predominant in polar solvents. This result indicates that β3-HPro is significantly less apt to form pseudo-γ-turns when compared to the γ-turn forming tendency of α-proline. The present study also shows that the interpretation of solution-phase VCD spectra of flexible molecules should be done with extra caution.

Original languageEnglish
Pages (from-to)13603-13615
Number of pages13
JournalPhysical Chemistry Chemical Physics
Volume12
Issue number41
DOIs
Publication statusPublished - Nov 7 2010

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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