Hydrogen Bond chiral separations

B. Feibush, Chiral separation of enantiomers via selector/selectand hydrogen bondings, Chirality 10 (1998), 382-395. 

Separation of enantiomers by physical or chemical methods requires the use of a chiral material, reagent, or catalyst. Both natural materials, such as polysaccharides and proteins, and solids that have been synthetically modified to incorporate chiral structures have been developed for use in separation of enantiomers by HPLC. The use of a chiral stationary phase makes the interactions between the two enantiomers with the adsorbent nonidentical and thus establishes a different rate of elution through the column. The interactions typically include hydrogen bonding, dipolar interactions, and n-n interactions. These attractive interactions may be disturbed by steric repulsions, and frequently the basis of enantioselectivity is a better steric fit for one of the two enantiomers. ... 

For example, only those dihydropyrimidines that contained a hydrogen-bonding donor at position 3 next to the chiral center were separated. Remarkably, dihydropyrimidines with non-substituted nitrogen atoms at positions 1 and 3 resulted in separations with longer retention times and decreased separation factors a. Increas-... 

The importance of steric and hydrogen bond interactions in chiral separations of nonaromatic samples... 

A number of ketones, pharmaceutical compounds, alcohols and hydroxy acids have also been resolved on this phase [724,765-767]. A chiral polysiloxane phase with tartramide substituents has been used for the separation of enantiomers capable of hydrogen bonding interactions with the stationary phase, such as enantiomers containing carboxylic, hydroxyl and amine functional groups [768]. 

Some practical applications of non-covalent interactions are also very interesting. The basis of the separation of enantiomers by the chromatographic method21 is the preferential interaction of one enantiomer of a substance with one enantiomer of another substance, which is usually part of the chiral stationary phase. Non-covalent interactions are more frequent hydrogen bonding, host-guest and donor-acceptor interactions. 

Affinity liquid chromatography and chiral separations (enantiomer separations) require similar analyte properties. The solutes may have interactions through hydrogen-bonding, ligand formation, or Coulombic forces with the surface of stationary phase materials or the sites of additives however, the selectivity is controlled by the steric effects of the structures of the analyte molecules and the recognition molecules (chiral selectors). 

In most cases, the chiral selector is simply added to the BGE. " Interactions between the analytes and the chiral selector will determine the stability of the diastereomeric complexes formed. The interactions involved in the chiral recognition process in CE are hydrophobic, electrostatic, Van der Waals and hydrogen bond-type interactions. Several reviews discuss the principles of electrophoretic chiral separations. 

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