Preparation of Silica Nanosprings Using Cationic Gelators as Template

Cationic cyclo(dipeptide) gelators 10mimClO4, 11mimClO4, and 11pyClO4 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.