Enantioselective Collision-Activated Dissociation of Gas-Phase Tryptophan Induced by Chiral Recognition of Protonated L-Alanine Peptides.
Enantioselective dissociation in the gas phase is important for enantiomeric enrichment and chiral transmission processes in molecular clouds regarding the origin of homochirality in biomolecules. Enantioselective collision-activated dissociation (CAD) of tryptophan (Trp) and the chiral recognition ability of L-alanine peptides (L-Alan; n = 2-4) were examined using a linear ion trap mass spectrometer. CAD spectra of gas-phase heterochiral H+(D-Trp)(L-Alan) and homochiral H+(L-Trp)(L-Alan) noncovalent complexes were obtained as a function of the peptide size n. The H2O-elimination product was observed in CAD spectra of both heterochiral and homochiral complexes for n = 2 and 4, and in homochiral H+(L-Trp)(L-Ala3), indicating that the proton is attached to the L-alanine peptide, and H2O loss occurs from H+(L-Alan) in the noncovalent complexes. H2O loss did not occur in heterochiral H+(D-Trp)(L-Ala3), where NH3loss and (H2O + CO) loss were the primary dissociation pathways. In heterochiral H+(D-Trp)(L-Ala3), the protonation site is the amino group of D-Trp, and NH3loss and (H2O + CO) loss occur from H+(D-Trp). L-Ala peptides recognize D-Trp through protonation of the amino group for peptide size n = 3. NH3loss and (H2O + CO) loss from H+(D-Trp) proceeds via enantioselective CAD in gas-phase heterochiral H+(D-Trp)(L-Ala3) at room temperature, whereas L-Trp dissociation was not observed in homochiral H+(L-Trp)(L-Ala3). These results suggest that enantioselective dissociation induced by chiral recognition of L-Ala peptides through protonation could play an important role in enantiomeric enrichment and chiral transmission processes of amino acids.
Department of Chemistry, Osaka Prefecture University, Osaka, Japan. fujihara@c.s.osakafu-u.ac.jp.
Akimasa
A
Fujihara
Department of Chemistry, Osaka Prefecture University, Osaka, Japan.
Hiroki
H
Matsuyama
Department of Molecular Medicine, Osaka Medical Center and Research Institute for Matemal and Child Health, Osaka, Japan.
Michiko
M
Tajiri
Department of Molecular Medicine, Osaka Medical Center and Research Institute for Matemal and Child Health, Osaka, Japan.
Yoshinao
Y
Wada
Department of Chemistry, Osaka Prefecture University, Osaka, Japan.
Shigeo
S
Hayakawa
D000409:Alanine; D010455:Peptides; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D014364:Tryptophan
D010455:Peptides; D014364:Tryptophan; D000409:Alanine
Chiral transmission; Enantiomeric enrichment; Fragmentation; Mass spectrometry; Proton transfer