title: Investigation of Fragmentation of Tryptophan Nitrogen Radical Cation.
abstract: This work describes investigation of the fragmentation mechanism of tryptophan N-indolyl radical cation, H3N(+)-TrpN(•) (m/z 204) studied via DFT calculations and several gas-phase experimental techniques. The main fragment ion at m/z 131, shown to be a mixture of up to four isomers including 3-methylindole (3MI) π-radical cation, was found to undergo further loss of an H atom to yield one of the two isomeric m/z 130 ions. 3-Methylindole radical cation generated independently (via CID of [Cu(II)(terpy)3MI](•2+)) displayed gas-phase reactivity partially similar to that of the m/z 131 fragment, further confirming our proposed mechanism. CID of deuterated tryptophan N-indolyl radical cation (m/z 208) suggested that up to six H atoms are involved in the pathway to formation of the m/z 131 ion, consistent with hydrogen atom scrambling during CID of protonated Trp.
authors.affiliation: Department of Chemistry and Biochemistry, and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, IL, 60115, USA.
authors.forename: Andrii
authors.initials: A
authors.lastname: Piatkivskyi
authors.forename: Marshall
authors.initials: M
authors.lastname: Happ
authors.forename: Justin Kai-Chi
authors.initials: JK
authors.lastname: Lau
authors.forename: K W Michael
authors.initials: KW
authors.lastname: Siu
authors.forename: Alan C
authors.initials: AC
authors.lastname: Hopkinson
authors.forename: Victor
authors.initials: V
authors.lastname: Ryzhov
mesh_terms: D002412:Cations / Q000737:chemistry; D041961:Deuterium Exchange Measurement; D006859:Hydrogen / Q000737:chemistry; D013058:Mass Spectrometry; D008958:Models, Molecular; D009584:Nitrogen / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D002412:Cations; D006859:Hydrogen; D014364:Tryptophan; D009584:Nitrogen