title: Conformation-specific spectroscopy and photodissociation of cold, protonated tyrosine and phenylalanine.
abstract: We present here ultraviolet and infrared spectra of protonated aromatic amino acids in a cold, 22-pole ion trap. Ultraviolet photofragmentation spectra of protonated tyrosine and phenylalanine show vibronically resolved bands corresponding to different stable conformers: two for PheH+ and four in the case of TyrH+. We subsequently use the resolved UV spectra to perform conformer-specific infrared depletion spectroscopy. Comparison of the measured infrared spectra to density functional theory calculations helps assign the geometry of the various conformers, all of which exhibit NH...pi hydrogen bonds and NH...O=C interactions, with the COOH group oriented either anti or gauche to the aromatic ring. In both molecules the majority of the observed fragments result from dissociation on an excited electronic state. In TyrH+, different conformers excited with practically the same energy exhibit different fragmentation patterns, suggesting that the excited-state dynamics depend upon conformation.
authors.affiliation: Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédérale de Lausanne, EPFL SB ISIC LCPM, Station 6, CH-1015 Lausanne, Switzerland. jaime.stearns@epfl.ch
authors.forename: Jaime A
authors.initials: JA
authors.lastname: Stearns
authors.forename: Sébastien
authors.initials: S
authors.lastname: Mercier
authors.forename: Caroline
authors.initials: C
authors.lastname: Seaiby
authors.forename: Monia
authors.initials: M
authors.lastname: Guidi
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Boyarkin
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Rizzo
mesh_terms: D000465:Algorithms; D003080:Cold Temperature; D013058:Mass Spectrometry / Q000379:methods; D008968:Molecular Conformation; D010649:Phenylalanine / Q000737:chemistry* / Q000378:metabolism; D010777:Photochemistry; D011522:Protons; D013055:Spectrophotometry, Infrared / Q000379:methods; D014443:Tyrosine / Q000737:chemistry* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D011522:Protons; D014443:Tyrosine; D010649:Phenylalanine