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

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 N 2 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 ‐Δ S,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. Δ S,R (ΔH) = –12.64 ± 0.08 kJ mol ‐1 and Δ S,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.