Enantiomeric adsorption of lactic acid mixtures in achiral zeolites

We studied the adsorption of chiral mixtures of lactic acid in several zeolites. All zeolite systems showed either no selectivity or heteroselectivity in which the minority enantiomer is adsorbed by a higher fraction than its fraction in the reservoir. Analysis of the mechanism showed that none of the previously identified origins of enantioselective adsorption of scalemic mixtures apply to lactic acid. However, on the basis of the lack of any ordered distribution in the adsorbed phase, we postulate a new mechanism that is likely to be very generic for chiral adsorption processes that proceed via chaotic packing of the adsorbate molecules. The new mechanism can explain several characteristics of the adsorption data and hints at new prospective separation methods with a high potential for pharmaceutical applications.