title: Gas-phase ion chemistry of Glu/Met systems.
abstract: A combined chemical ionisation and tandem mass spectrometry (MS/MS) approach has been used for investigation of the gas-phase ion chemistry of systems containing the amino acids Glu and Met, and the dipeptides gamma-Glu-Met and Met-Glu. The metastable fragmentation of the protonated dimer, (Glu)2H(+), reveals an intracluster reaction leading to the elimination of the Glu residue. The main features of the ion-molecule reactions observed in the systems containing Glu and Glu + Met can be described in terms of sequential adduct formation. The results obtained for the thermal dehydration of Glu were used to rationalise the formation of the proton-bound structures (Glu-H2O...H(+)...(Glu-H2O) and (Glu-H2O)3-H(+). The adduct ions, [(Glu-H2O) + H + Glu](+) and [(Glu-H2O) + H + Met](+), and further association products were also observed. The results lead to a reconsideration of the structural aspects proposed earlier for these species in the sense that they suggest that the systems correspond to a mixture of isomeric covalent and proton-bound structures. The thermal effects on the decomposition of the neutral (gamma-Glu-Met) and its protonated form, (gamma-Glu-Met)H(+), at m/z 279 were investigated, and dramatic changes in the MI spectra of the m/z 279 ion with temperature were found. A mechanistic explanation for the observed evolution of higher mass ion peaks in the mass spectra is developed.
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland. wincel@ichf.edu.pl
authors.forename: H
authors.initials: H
authors.lastname: Wincel
authors.forename: R H
authors.initials: RH
authors.lastname: Fokkens
mesh_terms: D002138:Calibration; D004151:Dipeptides / Q000032:analysis* / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry*; D008715:Methionine / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D004151:Dipeptides; C406458:glutamylmethionine; C406459:methionylglutamic acid; D005973:Glutamine; D008715:Methionine