Chiral discrimination in host-guest supramolecular complexes. Understanding enantioselectivity and solid solution behaviors by using spectroscopic methods and chemical sensors.
Diastereomeric host-guest associations formed between permethylated-beta-cyclodextrin (TMbeta-Cd) and the two enantiomers of p-bromophenylethanol (pBrPE) were characterized in aqueous solution by NMR spectroscopy, revealing similar inclusion geometries and weak binding constants, whatever the guest configuration. These features were confirmed by hydrogenation experiments, and do not allow to account for the ability of TMbeta-Cd to resolve racemic pBrPE by successive crystallizations [Grandeury, A.; Petit, S.; Gouhier, G.; Agasse, V.; Coquerel, G. Tetrahedron: Asymmetry 2003, 14, 2143-2152]. The analysis, by means of solid-state NMR, oxidation experiments, and solubility measurements, of the two crystalline phases containing known proportions of guest enantiomers revealed identical inclusion geometries in a given phase, irrespective of the enantiomeric composition. The corresponding solid solutions were further characterized by the determination of an isothermal section (40 degrees C) in the relevant ternary phase diagram. It appears from all these data that chiral resolution mechanisms in this system can only be envisaged in terms of nucleation conditions of each crystal form (with its specific inclusion geometry) and enantiomeric recognition at crystal solution interfaces during the growth of each crystal packing.
Grandeury
Arnaud
A
Unité de Croissance Cristalline et de Modélisation Moléculaire, Sciences et Méthodes Séparatives, UPRES EA 3233, IRCOF, Université de Rouen, F-76821 Mont Saint-Aignan Cedex, France.
Condamine
Eric
E
Hilfert
Liane
L
Gouhier
Géraldine
G
Petit
Samuel
S
Coquerel
Gérard
G
D000438:Alcohols / Q000737:chemistry; D003460:Crystallization; D006859:Hydrogen / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008745:Methylation; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D010084:Oxidation-Reduction; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives / Q000737:chemistry; D012996:Solutions; D012997:Solvents; D013237:Stereoisomerism; D047392:beta-Cyclodextrins / Q000737:chemistry
C522554:1-(4-bromophenyl)ethanol; D000438:Alcohols; D012996:Solutions; D012997:Solvents; D047392:beta-Cyclodextrins; D009532:Nickel; D006859:Hydrogen; D010626:Phenylethyl Alcohol