Molecularly imprinted organic–inorganic hybrid membranes for selective separation of phenylalanine isomers and its analogue

A novel kind of molecularly imprinted organic–inorganic hybrid membrane, using sodium alginate (SA) and 3-aminopropyltriethoxysilane (APTES) as the organic and inorganic phase, respectively, was prepared and investigated for the optical resolution of chiral isomers. The hybrid membrane was prepared in an aqueous environment with the presence of d-phenylalanine (d-Phe) as imprinting templates, and the silica phase was introduced in the alginate matrix by sol–gel process of APTES. It was found by FT-IR and SEM–EDX characterizations that strong covalent bonds were formed between the organic and inorganic phases, and silica was homogenously distributed in the matrix. These molecularly imprinted SA–APTES hybrid membranes showed chiral separation ability towards the d,l-Phe isomers with a maximum selectivity (αD/L) of 1.8 at 40% APTES content. The recognition mechanism was tentatively analyzed and discussed based on permeation and binding experiments. The separation ability of the above hybrid membranes toward d-Phe and its analogue, d-tyrosine (d-Tyr), was also investigated, and a separation factor of up to 2.9 was achieved.