Preparative-Scale Separation of Enantiomers Using Intercalated -Zirconium Phosphate

New lamellar compounds that have potential utility in preparative-scale enantiomeric separations were developed by combining principles from solid-state and molecular hostguest chemistry. Intercalation of α-zirconium phosphate (α-ZrP) by a cationic chiral -acceptor produces a solid that selectively binds one enantiomer of a π-donor analyte from a racemic solution. Both crystalline and semicrystalline α-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 singlepass 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.