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Folding Structures of Isolated Peptides as Revealed by Gas‐Phase Mid‐Infrared Spectroscopy
Author(s) -
Bakker Joost M.,
Plützer Christian,
Hünig Isabel,
Häber Thomas,
Compag Isabelle,
von Helden Gert,
Meijer Gerard,
Kleinermanns Karl
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400345
Subject(s) - conformational isomerism , chemistry , hydrogen bond , intramolecular force , van der waals force , infrared spectroscopy , folding (dsp implementation) , crystallography , chromophore , peptide , resonance (particle physics) , spectroscopy , infrared , amide , density functional theory , stereochemistry , computational chemistry , photochemistry , molecule , organic chemistry , biochemistry , physics , particle physics , optics , electrical engineering , engineering , quantum mechanics
To understand the intrinsic properties of peptides, which are determined by factors such as intramolecular hydrogen bonding, van der Waals bonding and electrostatic interactions, the conformational landscape of isolated protein building blocks in the gas phase was investigated. Here, we present IR‐UV double‐resonance spectra of jet‐cooled, uncapped peptides containing a tryptophan (Trp) UV chromophore in the 1000–2000 cm −1 spectral range. In the series Trp, Trp‐Gly and Trp‐Gly‐Gly (where Gly stands for glycine), the number of detected conformers was found to decrease from six (Snoek et al., PCCP, 2001 , 3 , 1819) to four and two, respectively, which indicates a trend to relaxation to a global minimum. Density functional theory calculations reveal that the OH in‐plane bending vibration, together with the NH in‐plane bending and the peptide CO stretching vibrations, is a sensitive probe to hydrogen bonding and, thus, to the folding of the peptide backbone in these structures. This enables the identification of spectroscopic fingerprints for the various conformational structures. By comparing the experimentally observed IR spectra with the calculated spectra, a unique conformational assignment can be made in most cases. The IR‐UV spectrum of a Trp‐containing nonapeptide (Trp‐Ala‐Gly‐Gly‐Asp‐Ala‐Ser‐Gly‐Glu) was recorded as well and, although the IR spectrum is less well‐resolved (and it probably results from different isomers), groups of amide I (peptide CO stretching) and amide II (NH in‐plane bending) bands can still be recognised, in agreement with predictions at the AM1 level.