A computational study of enantioselective adsorption in a homochiral metal-organic framework

The potential application of a homochiral metal-organic framework (MOF) made from cadmium corners and BINOL-type linkers for enantioselective separations of chiral hydrocarbons was investigated using grand canonical Monte Carlo simulations. Adsorption of racemic mixtures of (R,S)-1,3-dimethyl-1,2-propadiene, (R,S)-1,2-dimethylcyclobutane and (R,S)-1,2-dimethylcyclopropane was simulated. The results show that an enantiomeric excess (ee) of over 50% can be achieved for 1,3-dimethyl-1,2-propadiene, while more moderate ee values were observed for the cyclic compounds. The adsorption sites, diastereomeric complexes and adsorption energies were analysed to understand the enantioselective adsorption. It is shown that the small zigzag pores of the homochiral MOF account primarily for the enantioselective adsorption, whereas the larger helical pores show almost no enantioselectivity. The results also demonstrate that both intrinsic enantioselectivity and accessibility of the adsorption sites are important for the overall enantioselective separation.