Separation of Enantiomers by Inclusion Gas Chromatography: On the Influence of Water in the Molecular Complexation of Methyl 2‐Chloropropanoate Enantiomers and the Modified γ‐Cyclodextrin Lipodex‐E |
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Authors: | Alessandro Mandoli Volker Schurig |
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Institution: | 1. Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Pisa, Italy;2. Institut für Organische Chemie, Universit?t Tübingen, Tübingen, Germany |
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Abstract: | A profound influence of water has previously been detected in the complexation of the enantiomers of methyl 2‐chloropropanoate (MCP) and the chiral selector octakis(3‐O‐butanoyl‐2,6‐di‐O‐pentyl)‐γ‐cyclodextrin (Lipodex‐E) in NMR and sensor experiments. We therefore investigated the retention behavior of MCP enantiomers on Lipodex‐E by gas chromatography (GC) under hydrous conditions. Addition of water to the N2 carrier gas modestly reduced the retention factors k of the enantiomers, notably for the second eluted enantiomer (S)‐MCP. This resulted in an overall decrease of enantioselectivity ‐ΔS,R(ΔG) in the presence of water. The effect was fully reversible. Consequently, for a conditioned column in the absence of residual water, the determined thermodynamic data, i.e. ΔS,R(ΔH) = –12.64 ± 0.08 kJ mol‐1 and ΔS,R(ΔS) = –28.18 ± 0.23 J K‐1 mol‐1, refer to a true 1:1 complexation process devoid of hydrophobic hydration. Chirality 28:124–131, 2015. © 2015 Wiley Periodicals, Inc. |
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Keywords: | enantioselective inclusion gas chromatography methyl 2‐chloropropanoate Lipodex‐E influence of water on molecular complexation |
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