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.
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
MANDOLI, ALESSANDRO
;
2016-01-01
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.File | Dimensione | Formato | |
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