title: Secondary Structures in Phe-Containing Isolated Dipeptide Chains: Laser Spectroscopy vs Quantum Chemistry.
abstract: The intrinsic conformational landscape of two phenylalanine-containing protein chain models (-Gly-Phe- and -Ala-Phe- sequences) has been investigated theoretically and experimentally in the gas phase. The near UV spectroscopy (first ππ* transition of the Phe ring) is obtained experimentally under jet conditions where the conformational features can be resolved. Single-conformation IR spectroscopy in the NH stretch region is then obtained by IR/UV double resonance in the ground state, leading to resolved vibrational spectra that are assigned in terms of conformation and H-bonding content from comparison with quantum chemistry calculations. For the main conformer, whose UV spectrum exhibits a significant Franck-Condon activity in low frequency modes involving peptide backbone motions relative to the Phe chromophore, excited state IR spectroscopy has also been recorded in a UV/IR/UV experiment. The NH stretch spectral changes observed in such a ππ* labeling experiment enable us to determine those NH bonds that are coupled to the phenyl ring; they are compared to CC2 excited state calculations to quantify the geometry change upon ππ* excitation. The complete and consistent series of data obtained enable us to propose an unambiguous assignment for the gallery of conformers observed and to demonstrate that, in these two sequences, three conceptually important local structural motifs of proteins (β-strands, 27 ribbons, and β-turns) are represented. The satisfactory agreement between the experimental conformational distribution and the predicted landscape anticipated from the DFT-D approach demonstrates the capabilities of a theoretical method that accounts for dispersive interactions. It also shows that the flaws, inherent to a resonant two-photon ionization detection scheme, often evoked for aromatic chromophores, do not seem to be significant in the case of Phe.
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Yohan
authors.initials: Y
authors.lastname: Loquais
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Gloaguen
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Sana
authors.initials: S
authors.lastname: Habka
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Vanesa
authors.initials: V
authors.lastname: Vaquero-Vara
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Brenner
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Tardivel
authors.affiliation: †CEA, IRAMIS, Laboratoire Interactions, Dynamique et Lasers, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.|‡CNRS, INP, Laboratoire Francis Perrin, URA 2453, CEA Saclay, Bât 522, 91191 Gif-sur-Yvette, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Mons
mesh_terms: D007834:Lasers; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D010649:Phenylalanine / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011789:Quantum Theory; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
chemical_list: D010455:Peptides; D010649:Phenylalanine