Anionic surfactant templated chiral nanospheres and their enantioselective adsorption

Abstract

Monodispersed chiral mesoporous spheres of nanometer size with high specific area and good thermal stability were synthesized using the chiral anionic surfactant (N-palmitoyl-L-phenylalanine) as a template according to the co-structure directing agent (CSDA) method. The resulting mesoporous nanospheres were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray powder diffraction (XRD) and nitrogen sorption experiments. The particle distribution was 190–210 nm with pore diameters of 3–4 nm. The enantioselective ability of this chiral mesoporous silica, after extraction of the chiral surfactant, was investigated by the selective adsorption of enantiomers and racemic solutions of alanine. The chiral selective adsorbability of this material type was shown by the asymmetric preferential adsorption of alanine as observed using circular dichroism (CD) spectroscopy and was further verified in a racemic mixture of valine. It was found that the adsorption of L-alanine was higher than that of D-alanine on as-prepared chiral mesoporous materials with a chiral selectivity factor of 3.15, which generates new possibilities for enantiomeric separation and other enantioselective applications.