Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica

Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an L-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25-30 angstrom in diameter and surface areas above 1000 m(2)/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.