Distinction of Amino Acid Enantiomers Based on the Basicity of Their Dimers

• Published in: Analytical chemistry (Washington) Vol. 69; no. 9; pp. 1700 - 1705
• Main Authors: Vékey, Károly, Czira, Gábor
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.05.1997
• Subjects: Amino acids; Chemistry; Exact sciences and technology; Mass spectrometry; Organic chemistry; Reactivity and mechanisms; Energy spectrum; Protonated form; Investigation method; Molecular structure; Multicomponent mixture; Aminoacid; Enantiomer; Chiral compound; Dimer; Alkalinity; Experimental study; Mass spectrometry
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac960931m

Mixtures of several amino acid pairs, in all four chiral combinations, were studied. The protonated trimers (A2BH+) fragment, forming ABH+ and A2H+ dimers. Abundance ratios of these fragments were measured in the mass-analyzed ion kinetic energy spectra of the trimers. These were found to depend on the stereochemistry (homo- or heterochiral form) of the ABH+ dimer. The results were evaluated using the kinetic method, and the chiral discrimination was related to a difference in gas-phase basicity (GB) between the homo- and the heterochiral dimers. Four amino acid pairs (proline−tryptophan, phenylalanine−alanine, phenylalanine−proline, and phenylalanine−valine) were studied. Chiral discriminations were observed in all cases, relating to 0.4−4 kJ/mol differences in GB. The technique described here can generally be used to study enantiomers by mass spectrometry and is capable of reliably distinguishing energy differences as small as 0.2 kJ/mol in cluster ions.