title: Conformation-specific infrared and ultraviolet spectroscopy of tyrosine-based protonated dipeptides.
abstract: We present the spectroscopy and photofragmentation dynamics of two isomeric protonated dipeptides, H+AlaTyr and H+TyrAla, in a cold ion trap. By a combination of infrared-ultraviolet double resonance experiments and density functional theory calculations, we establish the conformations present at low temperature. Interaction of the charge at the N-terminus with the carbonyl group and the tyrosine pi-cloud seems to be critical in stabilizing the low-energy conformations. H+AlaTyr has the flexibility to allow a stronger interaction between the charge and the aromatic ring than in H+TyrAla, and this interaction may be responsible for many of the differences we observe in the former: a significant redshift in the ultraviolet spectrum, a much larger photofragmentation yield, fewer stable conformations, and the absence of fragmentation in excited electronic states.
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: 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: D000409:Alanine / Q000737:chemistry; D002627:Chemistry, Physical / Q000379:methods; D004151:Dipeptides / Q000737:chemistry; D004583:Electrons; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry / Q000379:methods; D013055:Spectrophotometry, Infrared / Q000379:methods; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D004151:Dipeptides; D010455:Peptides; D014443:Tyrosine; D000409:Alanine