Induction and detection of chirality in doped sol-gel materials: NMR and circular dichroism studies

We have studied diastereomeric chiral interactions within sols, gels and xerogels of silicas and derivatized silicas (20% phenylated and 10% octadecylated silicas) doped with the chiral surfactant (-)-N-dodecyl-N- methylephedrinium bromide (DMB). Two spectral methods - new in the context of chiral sol-gel materials - have been used for that purpose. In the first method, we were able to detect the diastereomeric interactions between DMB and each of the pure enantiomers of co-doped 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate using ³¹P-NMR spectroscopy. In the second method, we were able to obtain an induced circular dichroism (ICD) signal from the achiral dye Congo Red co-doped with DMB. NMR and ICD are complementary in understanding the way in which the chiral surfactant creates chiral environments inside the sol-gel materials. In particular, we provide ICD evidence that the silica network itself becomes chiral due to the entrapment of the chiral surfactant.