Journal
JOURNAL OF CHROMATOGRAPHY A
Volume 960, Issue 1-2, Pages 97-108Publisher
ELSEVIER
DOI: 10.1016/S0021-9673(02)00244-3
Keywords
enantiomer separation; chiral stationary phases, LC; temperature effects; apparent enantioselectivity; apparent thermodynamics; van't Hoff plots; cinchona alkaloids; amino acids
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The influence of temperature on the performance of an enantioselective anion-exchange type chiral selector (SO) was systematically investigated. The resolution of the enantiomers of 23 N-acylated amino acids (selectands, SAs) on a covalently immobilized quinine tert.-butylcarbamate chiral stationary phase (CSP) was studied under linear chromatographic conditions over a temperature range of 0-85 degreesC with hydro-organic buffers (pH(a) 6.0) as mobile phases. The apparent enantioseparation factors increased considerably at low column temperatures, indicating that enthalpic contributions are the dominating thermodynamic driving force for chiral recognition for all investigated SAs. Retention factors gave non-linear van't Hoff plots, while the corresponding apparent enantioseparation factors showed linear van't Hoff behavior. Correlations between magnitude and sign of the relative thermodynamic parameters of enantioselective adsorption (DeltaDeltaG, DeltaDeltaH and DeltaDeltaS) and specific structural features of the analytes, i.e., steric and electronic nature of the various side chains and the N-acyl groups, are discussed with the aim to rationalize their possible contributions to the overall chiral recognition. (C) 2002 Elsevier Science B.V. All rights reserved.
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