title: Single-conformation spectroscopy and population analysis of model γ-peptides: new tests of amide stacking.
abstract: Single-conformation ultraviolet and infrared spectra of a series of model gamma-peptides are reported, with the goal of providing new tests of amide stacking as an amide-amide binding motif. The data also serve to illustrate the power and challenges of carrying out single-conformation spectroscopy of neutral molecules of this size in the gas phase under jet-cooled conditions. Building on recent work on Ac-γ2-hPhe-NHMe (James et al., J. Am. Chem. Soc., 2009, 131, 14243), the effects of derivatization and H2O complexation on amide stacking are studied. Ac-γ2-hPhe-N(Me)2 shows only amide stacked structures, blocking the competing position for formation of an amide-amide H-bond. The Ac-γ2-hPhe-NHMe-H2O complex includes structures in which the H2O molecule forms a bridge between the two stacked amide planes, retaining and enhancing amide stacking. IR population transfer methods are also employed to study the dynamics of photodissociation of the amide stacked-H2O complex. Finally, IR ion-gain spectroscopy is introduced as a means of recording infrared spectra containing contributions from all conformers present, based on IR-induced broadening of the UV absorptions. Its role in estimating fractional abundances is tested on Ac-γ2-hPhe-NHMe.
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, USA.
authors.forename: Evan G
authors.initials: EG
authors.lastname: Buchanan
authors.forename: William H
authors.initials: WH
authors.lastname: James
authors.forename: Anna
authors.initials: A
authors.lastname: Gutberlet
authors.forename: Jacob C
authors.initials: JC
authors.lastname: Dean
authors.forename: Li
authors.initials: L
authors.lastname: Guo
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Zwier
mesh_terms: D000577:Amides / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002627:Chemistry, Physical; D003080:Cold Temperature; D005740:Gases; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism; D056951:Photoelectron Spectroscopy / Q000379:methods*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013055:Spectrophotometry, Infrared / Q000379:methods*; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000577:Amides; D005740:Gases; D009842:Oligopeptides; D014867:Water