Detailed experimental and theoretical analysis of chiral discrimination: Enantioselective binding of R/S methyl mandelate by β-Cyclodextrin

Abstract

Enantiodifferentiation of methyl mandelate by β-Cyclodextrin in the liquid phase is explored in detail. Temperature dependent studies using a β- cyclodextrin chiral stationary phase provided differential binding enthalpies and entropies. NMR studies revealed where around the host molecule the guest tends to reside. Molecular dynamics simulations correctly predict the retention order and provide an atomistic account of how chiral discrimination takes place. It is found that short range dispersion forces rather than long range coulombic forces are responsible for both complexation and for enantiodiscrimination. The intermolecular hydrogen bonds are not discriminating and the idea that a tight fit of included species within a cyclodextrin cavity be a requirement for chiral discrimination is questioned.