Understanding the Mechanism of Chirality Transfer in the Formation of a Chiral MCM-41 Mesoporous Silica

Recently, a series of chiral mesoporous silicas with various pore sizes and nanostructures (including chiral MCM-41, chiral SBA-15, and chiral SBA-16) have been successfully synthesized in our group by using achiral templates and a chiral cobalt complex as cotemplate. Enantioselective discrimination ability of these chiral materials was observed when they were applied on the controlled release of a chiral drug. The enantioselectivity of these silica materials was attributed to the local chirality at a molecular level on the pore wall surfaces. Nevertheless, the formation mechanism of local chirality, i.e., the chirality transferring from chiral cobalt complex to inorganic mesoporous silica matrix, remains indeterminate at this juncture. In this report, by tuning the synthesis parameters based on the previously reported method, chiral MCM-41 with left-handed enantiomeric excess in twisted hexagonal particle morphology was obtained. Enantioselective adsorption of racemic valine corroborated the general chirality of chiral MCM-41. The formation mechanism of chiral MCM-41 was determined by investigations on interactions among achiral surfactant, chiral cotemplate and silica with the help of vibrational circular dichroism spectroscopy and zeta potential measurements. We speculated that the chiral cobalt complex with a rigid propeller-like configuration and "planar" chirality incorporated into the micelle composed of achiral surfactants, directing the formation of chiral aggregation assembled by chiral cobalt complex and adjacent surfactants. Subsequently, the chiral aggregation transferred its chirality to the building blocks of mesoporous silica via electrostatic interaction.