Chiral Stationary Phases

Many chiral selectors are adsorbed or immobilized covalently on to liquid chromatography supports. The chiral stationary phases obtained are classified into two types with respect to their general structure. One type is based on synthetic or natural polymers, which are totally or intrinsically chiral; the other type is based on a chiral selector of low molecular weight. Chiral stationary phases can be further classified into five types based on the solute and chiral stationary-phase interactions:

• Type I: the diastereomeric complexes of the solute and chiral stationary phase are formed by attractive interactions such as hydrogen-bonding, n-n, dipole stacking, etc., between the solute and chiral stationary phase.

• Type II: the primary mechanism for the formation of the solute and chiral stationary phase complex is through attractive interactions, but inclusion complexes also play an important role.

• Type III: the solute enters into chiral cavities within the chiral stationary phase to form inclusion complexes.

• Type IV: the solute is a part of a diastereomeric metal complex; this is called chiral ligand exchange chromatography.

• Type V: the chiral stationary phase is a protein and the solute and chiral stationary phase complexes are based on combinations of hydrophobic, electrostatic and hydrogen-bonding interactions.

Table 2 shows commercially available chiral stationary phases which are classified into these five types.

n(ch3)2

n(ch3)2

o-Phthalaldehyde (OPA) 1-(9-Fluorenyl)ethyl chloroformate (FLEC) 1-(4-Dimethylamino-1-naphthyl)

ethylamine (DANE)

o-Phthalaldehyde (OPA) 1-(9-Fluorenyl)ethyl chloroformate (FLEC) 1-(4-Dimethylamino-1-naphthyl)

ethylamine (DANE)

1-(1-Naphthyl)ethyl isocyanate (NEIC) 2-Methyl-1,1'-binaphthalene-2'-carbonylcyanide

(methyl-BNCC)

1-(1-Naphthyl)ethyl isocyanate (NEIC) 2-Methyl-1,1'-binaphthalene-2'-carbonylcyanide

(methyl-BNCC)

Figure 1 Structure of reagents (see Table 1).

Figure 2 Structure of reagents (see Table 1).
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