Enantioselective adsorption and diffusion of S-/R-glycidol in homochiral zeolites: A molecular simulation study

As the first example of enantiopure homochiral zeolites, silicogermanates SU-32 can be synthesized in right- (SU-32a) or left-handed (SU-32b). These rare chiral zeolites provide beautiful benchmark structures to examine the microscopic properties of chiral molecules in the helical channels with only a single handedness. We report a molecular simulation study to investigate the enantioselective adsorption and diffusion of S-/R-glycidol enantiomers in SU-32a and SU-32b. S-glycidol is found to interact with SU-32a more strongly than R-glycidol and preferentially adsorbed in SU-32a, and the opposite is observed in SU-32b. The enantiomeric excess of S-/R-glycidol racemic mixture in SU-32a and SU-32b is up to 25% and slightly decreases with increasing temperature. For pure enantiomers, S-glycidol diffuses faster in SU-32a and slower in SU-32b, whereas the reverse is true for R-glycidol. The free energy analysis suggests that S-glycidol encounters a lower barrier to diffuse in SU-32a but a higher one in SU-32b. For S-/R-glycidol racemic mixture, the diffusion difference between two enantiomers becomes negligible as loading increases. This study reveals that enantiopure SU-32a and SU-32b have distinct enantioselectivity for glycidol enantiomers, particularly the selective adsorption, and might be useful for chiral separation. (C) 2010 Elsevier B.V. All rights reserved.