RESUMEN
An electrospray ionization mass spectrometric method for the simultaneous analysis of the enantiomeric excess of free amino acids, without chromatographic separation, was demonstrated using a quasi-racemic mixture of deuterium-labelled and unlabelled chiral copper(ii) complexes. This convenient method enables the simultaneous high-sensitivity determination of the enantiomeric excess of 12 amino acids.
RESUMEN
A series of copper(II) complexes with chiral tetradentate ligands, N,N'-ethylene- bis(S-amino acid methyl amide or methyl ester) prepared from S-alanine, S-phenylalanine, S-valine or S-proline, was generated in methanol. The copper complexes provided three component complexes in the presence of a free chiral amino acid. The enantioselectivity for the amino acid was evaluated by electrospray ionization-mass spectrometry coupled with the deuterium-labeled enantiomer method and these copper complexes were found to exhibit high enantioselectivity for free amino acids having bulky side chains. This result suggests that steric interaction between the tetradentate ligand and free amino acid was a major factor in chiral recognition. The copper complex with a chiral tetradentate ligand prepared from S-proline showed opposite enantioselectivity to copper complexes consisting of tetradentate ligands prepared from other S-amino acids. The conformational difference of the tetradentate ligand in the copper complex was found to be significant for enantioselectivity.
RESUMEN
By using electrospray ionization mass spectrometry coupled with the use of deuterium-labelled quasienantiomers, enantioselective coordination of a free amino acid as the second ligand of a copper(ii) complex with a novel chiral tetradentate ligand was evaluated quantitatively in a short measurement time.