Chemistry Reference
In-Depth Information
Fig. 27 Functionalization of SWCNTs with a PEG phospholipid for the conjugation of
thiol-siRNA through disulfide linkages
4.2.1 Endohedral Filling
Another interesting possibility that CNTs offer is that they can encapsulate
molecules or ions in their inner cavity and confine them. This fact could be useful,
for example, to protect the encapsulated materials from reactions in contact with the
atmosphere or, in a different approach, CNTs could behave as nanoreactors where
confined reactions can occur.
CNTs were first filled by fullerenes, azafullerenes, and endohedral metallo-
fullerenes producing peapod structures. Besides fullerenes, other organic
molecules have been confined such as conjugated dyes, ionic liquids, and
polymeric species. Moreover, inorganic substances such as iodide salts have
been encapsulated. An interesting example is the confinement of Gd
3+
ion
clusters within ultra-short SWCNTs; these new derivatives have been explored
as “nanocapsules” for Magnetic Resonance Imaging (MRI), exhibiting
efficiencies 40-90 times larger than any Gd
3+
-based contrast agent (CA) in
current clinical use [
127
].
4.3 Multifunctionalized Carbon Nanotubes
While scientists have shown that CNTs can be chemically modified, the integration
of these systems into functional materials is still a challenging task. The advantage
of a noncovalent attachment is that the perfect structure of the CNT is not damaged
and their properties remain intact. On the other hand, the covalent functionalization
offers the possibility to have functional groups strongly attached on the nanotube
surface, and therefore avoids the risk of desorption. Still, for some applications,
CNTs must be modified with more than one group and in these cases simultaneous
optimization of several functionalities is a demanding issue.
