Fascinating chiral information transfer to titania/silica from near to racemic compound self-organized from polyethyleneimine and tartaric acid

Abstract

In this work, chiroptical crystalline complexes of PEI/Tart (P/T) consisting of linear poly(ethylemeimine) (PEI) and an enantiomeric excess (ee) of tartaric acid (Tart) were used as chiral catalytic templates in the hydrolytic condensation of titanium bislactates and co-condensation of titanium bislactates and tetramethoxysilane for the preparation of chiral titania (TiO₂) and chiral titania/silica (TiO₂/SiO₂) hybrid. Different from the general case of enantiopure templates excelling in chiral transformation when compared to enantiomeric excess ones, P/T systems with different enantiomer ratios exhibited each activity in the transformation of their chiral information to the resulting minerals titania and titania/silica. Especially, the P/T complexes with ee only by ±4% (D/L = 52/48 or 48/52), which is near the racemic state (D/L = 50/50), served as excellent chiral catalytic templates to generate chiroptical titania and titania/silica with mirror relation of the CD signals. By means of DSC, XRD, SEM and DRCD techniques, the crystalline complexes of PEI/Tart (P/T), the as-prepared TiO₂@P/T and TiO₂/SiO₂@P/T, and the calcined TiO₂ and TiO₂/SiO₂ were thoroughly investigated and the mechanism of the chiral transformation from the enantiomeric excess of P/T to minerals was proposed.