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48
Chapter 4
Summary and Perspective
49
Chapter 4
50
Chapter 4
In the present thesis, a new binding mode of CDs other than cavity inclusion was
discovered by utilizing TEM observation, and it was applied to solubilize hydrophobic
material. Microscopic analysis has an advantage in the analysis of mixture compared with
spectroscopic analyses, which only give averaged information of mixture. Its application
to the detection of minor species in equilibrium revealed the rim binding complex of CDs.
The rim binding mode contributed to the CD binding similarly to cavity binding and
successfully solubilized nanocarbon in water.
In Chapter 3, I demonstrated solubilization and purification of NH aggregates
using CDs. NH aggregates contain horn-less impurity, which is co-generated in the
production of NH aggregates. All CDs efficiently dispersed NH aggregates in water by
binding to the apex of NHs, while glucose and amylose as a linear analog of CDs did not
disperse NH aggregates well. Solubilization with a- and b-CD showed that cavity binding
was not necessary for their action. Furthermore, binding to the apex of NHs achieved
purification of NH aggregates by leaving GBs precipitated in water. The investigation of
desorption of CDs from NH aggregates revealed that a- and b-CD detached faster than
g-CD. Therefore, a-CD was utilized for large-scale purification of NH aggregates by
centrifugation of water dispersion and purified 2.00 g of NH aggregates in moderate yield.
Non-selective purification by centrifugation of EtOH dispersion showed a different
fraction of NH aggregates were separated and suggested that purification with CDs were
based on the shape-recognition and not solely on the density of materials. Finally, purified
NH aggregates were successfully utilized in further functionalization.
51
Chapter 4
Cavity and
rim binding
1 wt% cyclodextrin
Carbon nanohorn
aggregate (NHa)
GB
as precipitate
Graphitic ballshaped impurity
(GB)
H2N NH2
NH2 NaNH2/
H 2N
liq NH3
H 2N
NHa NH
H 2N
NH2
H 2N
1) sonication
2) centrifuge
– GB
NHa
filtration/
water wash
water
NHa
NHa
amino-NHa
NHa solubilized in water
Figure 4-3. Solubilization and purification of NHa by binding of CDs to the apex of
NHs via cavity and rim binding followed by centrifugation and amination.
The application of electron microscopic analysis to an equilibrium system
enables us to investigate structure and differentiate each species present in the equilibrium.
This is in clear contrast to conventional spectroscopic analysis, which only gives averaged
information of the whole equilibrium. In the present study, we have demonstrated that a
combination of SMART-EM and the NH library provides a tool not only to isolate the
equilibrating species from solution for structure characterization but also to determine the
thermodynamics governing the equilibria. We anticipate the application of this tool for
thermodynamic and kinetic studies of various chemical events.
52
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