Amino acid modified molecular sieves with different pore size for chiral separation

Abstract

The pore size of porous materials is of great importance for controlling chiral separation of enantiomers. However, the roles of the porous dimension in determining the separating performance are still unclear, especially when pores are comparable with or slightly larger than the target enantiomers in size. Here, we detected the effect of the pore dimension on the chiral separation performances using organic-inorganic hybrid materials with the different porous sizes at the nanometric level, which bore a chiral selector and thus can selectively bind one of enantiomers. In this work, mesoporous molecular sieves, i.e., SBA-15, KIT-6 and MCM-41, chemically modified with a chiral selector, N-acyl-protected d-glutamic acid, were used to separate d- and l-phenylalanine, as the chiral probes. The structure of hybrid materials, together with raw materials and intermediates, were systematically characterized by TEM, EA, TGA, XRD, FT-IR, and so on. The influence of porous size on enantioseparation behaviors can be defined by comparing enantioseparation results among SBA-15, KIT-6 and MCM-41 based hybrid materials, since they have different inner diameters. Results show that the MCM-41 based hybrid material with a ˜1.1 nm inner diameter exhibits an extraordinary chiral resolution performance, having a greater enantioselectivity, compared with KIT-6 and SBA-15 based hybrid material with the diameter of ˜4.0 and 7.8 nm. Our findings demonstrate that the pore size plays an important role in the enantioselectivity of porous materials.