Chiral resolution by crystallization of host-guest supramolecular complexes |
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Authors: | Grandeury A Renou L Dufour F Petit S Gouhier G Coquerel G |
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Institution: | (1) Unité de Croissance Cristalline et de Modélisation Moléculaire (UC2M2), Sciences et Méthodes Séparatives (SMS), UPRES EA 2659, IRCOF, Université de Rouen, F-76821 Mont Saint-Aignan Cedex, France;(2) Degussa group, Rexim company, F-80400, Ham, France;(3) Laboratoire des Fonctions Azotées et Oxygénées Complexes, UMR 6014, IRCOF, Université de Rouen, F-76821 Mont Saint-Aignan Cedex, France |
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Abstract: | The crystallization behaviour and the physical characterization of supramolecular complexes formed between permethylated-α-cyclodextrin
(TMα-CD) and the enantiomers of phenylethanol (PE) are investigated. According to crystal structure analyses, complexes containing
the pure guest enantiomers are almost isomorphous, indicating that the host presents a poor ability to distinguish PE enantiomers
at a molecular level. Nevertheless, crystallizations from racemic PE in water induce an efficient chiral discrimination and
allow the enantio-separation of the guests despite the existence of a solid solution revealed by XRPD and coupled TG-DSC analyses.
The enantiodifferentiation is explained by solubility differences between the two diastereomeric complexes in the studied
temperature range. Moreover, it is shown that the diastereomeric complex TMα-CD/(S)-PE crystallizes in two distinct phases: a monohydrate and an anhydrous form, with a transition temperature close to 37°C.
The insertion of a water molecule in the crystals grown below 37°C does not involve any other change of the crystal packing
nor of the molecular conformation, but leads to different crystal growth mechanisms inducing different morphologies and distinct
thermal behaviours.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | solubility crystal structure solid solution chiral recognition mechanism enantioseparation host-guest inclusion permethylacted cyclodextrin |
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