 | Self-Assembly of Sugar-Based Gelators and Their Transcription into Silica Nanotube
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| | Jong Hwa Jung1)2)3) and Toshimi Shimizu1)2)3) |
| 1) CREST
2) JST, Nanoarchitectonics Research Center
3) AIST |
| | New sugar-based gelators 1-4 were synthesized, and their gelation ability was evaluated in organic solvents and water. 1 and 2 were found to gelate organic solvents as well as water in the presence of a small amount of alcoholic solvents whereas 3 (0.05 wt%) and 4 (0.05 wt%) can gelate water in the absence of any organic solvent. These results indicate that 1-4 can act as amphiphilic gelators. We characterized on superstructures of aqueous gels from 1-4 using SEM, TEM, NMR, IR, and XRD. The aqueous gels 1 and 2 formed a three-dimensional network with 20-500 nm diameter puckered fibrils. In 3, more interesting is the finding that the spheres are connected to one another like a pearl necklace. Presumably, this new class of cross-link in the present system can be also the origin of the gelation phenomena. In 4, an aqueous gel displays three-dimensional fiber structure with less than 100 nm of diameter. According to Powder XRD experiments, aqueous gels 1 and 2 maintain bilayered structures with 2.90 nm long ranges spacing. These give the first example and formation of well ordered bilayer-based aqueous gel. On the other hand, 3 and 4 formed by self-assembly in water as well as organic solvents showed 3.65 nm long range spacing, indicating that 3 and 4 formed a single layered structures. The XRD, FT-NMR, and FT-IR results strongly suggest that 1-4 are stabilized by a combination of the hydrogen-bonding, π-π interactions, and hydrophobic forces. Sol-gel transcription of tetraethoxysilane (TEOS) was carried out using an aqueous gel 1 as a template. After calcinations, the silica showed nanotube structure, which had 10-20 nm of inner diameters, 30-50 nm walls, and 1-2 μm. This finding implies the view that the nanofiber structure of an aqueous gel was successfully replicated into the silica nanotube by sol-gel transcription. |
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