PREPARATIVE-SCALE SEPARATION OF ENANTIOMERS USING INTERCALATED ALPHA-ZIRCONIUM PHOSPHATE

New lamellar compounds that have potential utility in preparative-scale enantiomeric separations were developed by combining principles from solid-state and molecular host-guest chemistry. Intercalation of alpha-zirconium phosphate (alpha-ZrP) by a cationic chiral pi-acceptor produces a solid that selectively binds one enantiomer of a pi-donor analyte from a racemic solution. Both crystalline and semicrystalline alpha-ZrP were investigated in order to determine whether crystallinity and particle size have an effect on this process. Under favorable conditions, preparative-scale separations can be achieved in a batchwise process by means of multiple passes through the intercalated solid. Even if scaled up for single-pass enantioseparation, these solids provide over 30 times the separation capacity per gram relative to brush-type chiral selectors immobilized on chromatographic silica. The intercalated solids were characterized by UV-visible and FT-IR spectroscopies and by powder X-ray diffraction. A dramatic concentration effect is seen in the enantioselective binding; at low concentration of the enantiomer which forms a complex with the intercalated chiral selector there is essentially no binding, while above 150 mM the intercalated chiral host-guest complex is formed almost quantitatively. The structural nature of this concentration dependence is discussed.