Enantioselective Collision-Activated Dissociation of Gas-Phase Tryptophan Induced by Chiral Recognition of Protonated l-Alanine Peptides

• Published in: Origins of life and evolution of biospheres 2017-06, Vol.47 (2), p.161-167
• Main Authors: Fujihara, Akimasa, Matsuyama, Hiroki, Tajiri, Michiko, Wada, Yoshinao, Hayakawa, Shigeo
• Format: Article
• Language: English
• Subjects: Alanine; Amino acids; Ammonia; Astronomy; Astrophysics and Astroparticles; Biochemistry; Biomedical and Life Sciences; Chirality; Clouds; Dissociation; Earth Sciences; Enantiomers; Gases; Hydrogen; Interstellar clouds; Ions; L-Alanine; Life Sciences; Observations and Techniques; Peptides; Phase transitions; Spectrometry, Mass, Electrospray Ionization; Stereoisomerism; Temperature effects; Tryptophan
• ISSN: 0169-6149; 1573-0875
• DOI: 10.1007/s11084-016-9511-4

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 -Ala n ; n  = 2–4) were examined using a linear ion trap mass spectrometer. CAD spectra of gas-phase heterochiral H + ( d -Trp)( l -Ala n ) and homochiral H + ( l -Trp)( l -Ala n ) noncovalent complexes were obtained as a function of the peptide size n . The H 2 O-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 -Ala 3 ), indicating that the proton is attached to the l -alanine peptide, and H 2 O loss occurs from H + ( l -Ala n ) in the noncovalent complexes. H 2 O loss did not occur in heterochiral H + ( d -Trp)( l -Ala 3 ), where NH 3 loss and (H 2 O + CO) loss were the primary dissociation pathways. In heterochiral H + ( d -Trp)( l -Ala 3 ), the protonation site is the amino group of d -Trp, and NH 3 loss and (H 2 O + CO) loss occur from H + ( d -Trp). l -Ala peptides recognize d -Trp through protonation of the amino group for peptide size n  = 3. NH 3 loss and (H 2 O + CO) loss from H + ( d -Trp) proceeds via enantioselective CAD in gas-phase heterochiral H + ( d -Trp)( l -Ala 3 ) at room temperature, whereas l -Trp dissociation was not observed in homochiral H + ( l -Trp)( l -Ala 3 ). 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.