L- and D-proline adsorption by chiral ordered mesoporous silica.

Chiral ordered mesoporous silica (COMS) was synthesized in the presence of amino acid proline by combining tetraethyl orthosilicate and quaternized aminosilane silica sources. The as-prepared materials were activated by calcination or microwave chemical extraction to remove the organic templates. The powder X-ray diffraction and N2 adsorption characterization revealed in COMS the structural and textural features of MCM-41-type silica. The chirality of the material was disclosed by mixed and separate L- and D-proline adsorption on the COMS prepared with L-proline (L-Pro-COMS) and D-proline (d-Pro-COMS). It was found that the maximum L-proline and D-proline adsorption capacities on L-Pro-COMS were ca. 2.3 and 0.6 mmol/g, respectively, while the adsorption of D-proline was higher than that of l-proline on d-Pro-COMS. Finally, both activation routes yielded enantioselective silicas able to separate proline racemate.