Preparation of silica nanosprings using cationic gelators as template

Cationic cyclo(dipeptide) gelators 10mimClO(4), 11mimClO(4), and 11pyClO(4) were synthesized as templates for the sol-gel transcription reaction of alkoxysilanes. They were able to cause physical opaque gels in alcohols such as methanol, ethanol, and 1-propanol. Three-dimensional fibrous networks responsible for physical gelation were found in SEM images of gels. Sol-gel transcription reactions using the self-assemblies of three gelators as the templates were carried out in the presence of propylamine as a catalyst. When tetraethoxysilane (TEOS) was selected as a precursor, three kinds of morphologies, such as inner-helical nanotubes, right-handed nanobundles, and right-handed helical nanosprings were observed by electron microscopy. The helical nanosprings were preferentially formed as compared with nanotubes and nanobundles. On the other hand, the sol-gel polymerization of bis(triethoxysilyl)methane, 1,2-bis(triethoxysilyl)ethane, and 1,4-bis(triethoxysilyl)benzene as precursors gave nanoballs instead of tubular structures. When tetrabutylammonium fluoride (TBAF) was used as a catalyst, a helical tubular structure coated by silica nanoballs was identified.