Chemistry Reference
In-Depth Information
d
n
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r
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n
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Chart 8.9
molecules. Removal of the HDGA from inside resulted in the formation of
nanotubes with propylamine groups of APES in them. Interestingly, such
nanotubes show chirality (M- and P-chirality) from their inner walls that was
established by dispersing SiNTs fabricated from L-HDGA in water containing
tetraphenylporphine tetrasulfonic acid (TPPS). TPPS adsorbed within the
SiNTs showed both J and H aggregated bands at 490 and 435 nm and a
negative cotton effect in a circular dichroism (CD) study suggesting that
supramolecular chirality of TPPS was induced (Figure 8.5a). However,
HDGA-capped SiNTs upon dispersion into the TPPS solution did not exhibit
any kind of aggregation or CD signals. This result indicated that the chirality of
the inner wall of the SiNTs was controlled by the chiral gelator molecules. As
expected a mirror-imaged CD spectrum was obtained when SiNTs fabricated
from D-HDGA hydrogel were used. Similarly, when azobenzene was loaded
into the inner walls of the SiNTs, the chirality of the inner walls was transferred
to these azobenzene assemblies through p-p stacking, as confirmed from the
corresponding CD study (Figure 8.5b).
Nakano and coworkers reported the synthesis of fluorocarbon functionalised
silica nanotubes by a perfluoroalkyl chain-containing organogelator (22)asa
template (Chart 8.10). The sol-gel condensation was carried out using a
mixture of TEOS and fluorocarbon functionalised triethoxysilanes (23a-d,
Chart 8.10) in the presence of organogelator (22).
49
The silica obtained after
sol-gel polymerisation revealed a homogeneous tubular structure indicating
effective transcription of fibrillar structure of 22 to the final silica structure. The
presence of functionalised triethoxysilane was found to be crucial for successful
transcription as the polycondensation of only TEOS or trialkoxysilanes
possessing a long alkyl chain instead of the perfluoroalkyl chain resulted in
the formation of granular silica. The fluorocarbon-functionalised
trialkoxysilanes were absorbed onto the fibres of gelator 22 through the
aggregation of perfluoroalkyl chains between alkoxysilanes and started to
condense, resulting in the formation of the fluorocarbon-functionalised silica
tube. The chain length of the fluorocarbon functionalised triethoxysilanes also
played a role in transcription. Tubular silica structures were obtained with
F6-TEOS, F8-TEOS and F10-TEOS, whereas granular silica was obtained with
F4-TEOS.
In all the examples discussed above, the structure of the nanomaterials was
controlled by the addition of an external organic template that directs the
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