Sidechain Modulation of Responsive Metal-Organic Framework Pore Chirality for Enhanced Enantioseparation.

The selective separation of enantiomers is important for industrial technologies such as pharmaceuticals, biotechnology, and agrochemicals. Chiral porous materials have been used as the stationary phase for the chromatographic separation of enantiomers; however, they lack synthetic and performance designability. Here we present a new chiral metal-organic framework with excellent chromatographic enantioseparation performance for a family of aromatic chiral molecules. This material has been developed by diversifying the amino acid sidechains appended to an underlying common structural framework. The structure of the framework places the bulky isopropyl sidechain of L-valine in the one-dimensional pore channels characteristic of the materials family, modulating the accessible space to emphasize the helical shape of the channels. The dimensions of the pores are adapted to those of guests, through conformational flexibility directed by the sidechain, creating appropriate adsorption sites for functionalized aromatic guests. This porous framework affords superior enantioseparation performance compared to the same underlying framework decorated with the shorter methyl sidechain. These results demonstrate that the structure and porosity of dynamic chiral metal-organic frameworks can be tailored using amino acid-derived linkers and enhance the enantiomeric separations through stimulation of conformational flexibility.