title: Abundant dipositively charged protonated a2 and a3 ions from diproline and triproline.
abstract: Abundant (a(2) + H)(2+) from diproline and (a(3) + H)(2+) from triproline were observed via collisionally activated charge disproportionation of [La(peptide)(CH(3)CN)(1,2)](3+). These small, dipositive ions with the charges formally located on the peptide backbone are stabilized by charge delocalization onto the pyrrolidine-derived rings, making their formation competitive against other monopositive ions. The (a(2) + H)(2+) and (a(3) + H)(2+) ions from diproline and triproline are major products in contrast with those derived from triglycine, whose unprecedented and surprising observations were recently reported ( Shi et al. Angew. Chem., Int. Ed. 2008 , 47 , 8288 - 8291 ).
authors.affiliation: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3.
authors.forename: Junfang
authors.initials: J
authors.lastname: Zhao
authors.forename: Chi-Kit
authors.initials: CK
authors.lastname: Siu
authors.forename: Tujin
authors.initials: T
authors.lastname: Shi
authors.forename: Alan C
authors.initials: AC
authors.lastname: Hopkinson
authors.forename: K W Michael
authors.initials: KW
authors.lastname: Siu
mesh_terms: D003198:Computer Simulation; D006860:Hydrogen Bonding; D007477:Ions / Q000737:chemistry; D007811:Lanthanum / Q000737:chemistry*; D008956:Models, Chemical; D009842:Oligopeptides / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D011522:Protons
chemical_list: D007477:Ions; D009842:Oligopeptides; D009942:Organometallic Compounds; D011522:Protons; D007811:Lanthanum; D011392:Proline