Enantiomer recognition hydrogen bonding

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). 

The inclusion of enantiomers into the chiral cavities of the network is supposed to be the main chiral recognition mechanism. Moreover, hydrogen bonding between polar groups of the solutes and the amide groups of the polymers are also assumed to participate in the chiral recognition process. Apolar mobile phases such as hexane-dioxane and toluene-dioxane mixtures are therefore commonly used with this type of CSPs. 

A significant ability to discriminate between chiral amines based on the quenching of S-di-2-naphthylprolinol fluorescence emission was reported by Diamond et al. [32], fl-Phenylethylamine (PEA) was seen to have a much greater efficiency as a quencher than the S-enantiomer. l- and D-norephedrine, which have structural conformation similarities to PEA, were also observed to have an enantiomeric selectivity. The mechanism of chiral recognition is proposed to be a combination of hydrogen bonding and 3D chirally restricted space. 

In the case of lipases and esterases, chiral recognitions are not so strict. Both enantiomers were incorporated to the enzyme to form the substrate-enzyme complex. However, the slow reacting enantiomer lacked the necessary hydrogen-bonding interaction, for example in the hydrolysis of menthol acetate, between the substrate menthol and the enzyme histidine group for the reaction to proceed further (Figure 3(b)).2 3 The explanation was also supported by the observation in the esterification reaction of 1-phenylethanol by lipases.4 Km values of the slow and fast reacting... 

Analytical Properties Separation of amino acid enantiomers good chiral recognition of A/-acetyl amino acid methyl esters depends on hydrogen bond interactions hexane with isopropanol modifier has been used as the liquid phase usually prepared on LiChrosorb (10 pm)... 

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