Chiral separation of amino acids by copper(II) complexes of tetradentate diaminodiamido-type ligands added to the eluent in reversed-phase high-performance liquid chromatography: a ligand exchange mechanism

Citation
G. Galaverna et al., Chiral separation of amino acids by copper(II) complexes of tetradentate diaminodiamido-type ligands added to the eluent in reversed-phase high-performance liquid chromatography: a ligand exchange mechanism, J CHROMAT A, 922(1-2), 2001, pp. 151-163
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry & Analysis","Spectroscopy /Instrumentation/Analytical Sciences
Journal title
JOURNAL OF CHROMATOGRAPHY A
ISSN journal
0021-9673 → ACNP
Volume
922
Issue
1-2
Year of publication
2001
Pages
151 - 163
Database
ISI
SICI code
0021-9673(20010713)922:1-2<151:CSOAAB>2.0.ZU;2-T
Abstract
In this paper we report a study on the mechanism of the enantiomeric separa tion of unmodified D,L-amino acids in RP-HPLC by copper(II) complexes of tw o tetradentate diaminodiamido ligands, (S,S)-N,N ' -bis(phenylalanyl)ethane diamine (PheNN-2) and (S,S)-N,N ' -bis(methylphenylalanyl)ethane (Me(2)PheN N-2), added to the eluent. The aim is to investigate whether and how a copp er(II) complex with no free equatorial positions can perform chiral discrim ination of bidentate analytes such as unmodified amino acids. The problem i s approached in a systematic way by: (a) varying the different chromatograp hic parameters (pH, selector concentration, eluent polarity); (b) performin g chiral separation with the selector adsorbed on the stationary phase; (c) studying the ternary complex formation of these ligands with D- and L-amin o acids in solution by glass electrode potentiometry and electrospray ioniz ation MS. All the experimental data are consistent with a mechanism of chir al recognition, based on ligand exchange, which involves as selectors the s pecies [Cu2L2H-2](2+) and [CuLH-2] and proceeds by displacement of two bind ing sites from the equatorial positions, giving rise to the ternary species [CuLA](+) and [CuLH(-1)A]. The most important factor responsible for chira l discrimination seems to be the affinity of the diastereomeric ternary com plexes for the stationary phase since no enantioselectivity is observed in solution. (C) 2001 Elsevier Science B.V. All rights reserved.