title: Spectroscopy of mobility-selected biomolecular ions.
abstract: We describe here experiments that combine differential ion mobility, which separates conformational isomers of biomolecular ions, with electronic spectroscopy in a cold, radio-frequency ion trap. Although the low temperature attainable in a cold ion trap greatly simplifies the electronic spectra of large molecules, conformational heterogeneity can still be a significant source of congestion, complicating spectroscopic analysis. We demonstrate here that using differential ion mobility to separate gas-phase peptide conformers before injecting them into a cold ion trap allows one to decompose a dense spectrum into contributions from different conformational families. In the inverse sense, cold ion spectroscopy can be used as a conformation-specific detector for ion mobility, allowing one to separate an unresolved peak into contributions from different conformational families. The doubly protonated peptide bradykinin serves as a good test case for the marriage of these two techniques as it exhibits a considerable degree of conformational heterogeneity that results in a highly congested electronic spectrum. Our results demonstrate the feasibility and advantages of directly coupling ion mobility with spectroscopy and provide a diagnostic of conformational isomerization of this peptide after being produced in the gas phase by electrospray.
authors.affiliation: Laboratoire de Chimie Physique Moléculaire, Ecole Polytechnique Fédérale de Lausanne, Station 6, CH-1015 Lausanne, Switzerland.
authors.forename: Georgios
authors.initials: G
authors.lastname: Papadopoulos
authors.forename: Annette
authors.initials: A
authors.lastname: Svendsen
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Boyarkin
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Rizzo
mesh_terms: D001920:Bradykinin / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D002627:Chemistry, Physical; D003080:Cold Temperature; D005740:Gases / Q000737:chemistry; D007477:Ions / Q000032:analysis / Q000737:chemistry*; D007536:Isomerism; D013058:Mass Spectrometry / Q000379:methods*; D008968:Molecular Conformation; D009038:Motion; D010455:Peptides / Q000032:analysis / Q000737:chemistry*; D011522:Protons; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D005740:Gases; D007477:Ions; D010455:Peptides; D011522:Protons; D001920:Bradykinin