title: Conformations and vibrational spectra of a model tripeptide:  change of secondary structure upon micro-solvation.
abstract: Mid-infrared (IR) hole burning spectra of the model tripeptide Z-Aib-Pro-NHMe (Z = benzyloxycarbonyl) in gas phase and its micro-clusters with one and two methanol molecules are presented. To establish a relation between experimental spectra and the underlying conformations, calculations at the DFT [B3LYP/6-311++G(d,p)] level of theory are performed. In particular, the intra-peptide and the peptide-methanol hydrogen bonds can be identified from spectral shifts in the amide I, II, and III regions. While the unsolvated tripeptide as well as its one-methanol cluster prefer a gamma-turn structure, a beta-turn structure is found for the two-methanol cluster, in agreement with previous condensed phase studies. Comparison of measured and simulated spectra reveals that the favorable methanol binding sites are at the head and tail parts of the tripeptide. The interconversions between gamma-turn and beta-turn structures are governed by potential barriers below 10 kJ mol(-1) inside one of the low energy basins of the potential energy surface.
authors.affiliation: Institut für Mathematik, Freie Universität Berlin, Arnimallee 6, D-14195 Berlin, Germany. hui.zhu@fu-berlin.de
authors.forename: Hui
authors.initials: H
authors.lastname: Zhu
authors.forename: Martine
authors.initials: M
authors.lastname: Blom
authors.forename: Isabel
authors.initials: I
authors.lastname: Compagnon
authors.forename: Anouk M
authors.initials: AM
authors.lastname: Rijs
authors.forename: Santanu
authors.initials: S
authors.lastname: Roy
authors.forename: Gert
authors.initials: G
authors.lastname: von Helden
authors.forename: Burkhard
authors.initials: B
authors.lastname: Schmidt
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012995:Solubility; D013055:Spectrophotometry, Infrared
chemical_list: D009842:Oligopeptides