Endohedral functionalization

Endohedral functionalization of CNTs is the filling of the tubes with various atoms or small molecules [254]. The internal cavity of CNTs (1-2 nm in diameter) provides space for the accommodation of guest molecules [254-260], Even small proteins and other biomolecules [207, 208, 261] and oligonucleotides [262] have been trapped in the nanotube cavity. In 1998, Luzzi s group [263] for the first 

The incorporation of guest molecules can be achieved during their growth or is executed at defect sites and holes via wet chemistry, by surface diffusion and gas-phase transport. Encapsulated fullerenes tend to form chains that are coupled by van der Waals forces. Upon annealing, the encapsulated fullerenes coalesce in the interior of the SWCNTs, resulting in pill-shaped, concentric, endohedral capsules a few nanometers in length [265], The progress of such reactions inside the tubes could be monitored in real time by use of HR-TEM [266], 

In the class of metallofullerene peapods, in addition to Gd Cg2-containing peapods (Fig. 1.22) [267], also Dy C82-, La Cg2- and Sm Cg2-containing peapods and dimetallofullerene-containing peapods with peas of the kind of Ti2 Cgo, La2 Cg0 and Gd2 C92 have been synthesized (see the references in [254]). 

In addition to doping with fullerenes, SWCNTs can also be filled with molecules such as ferrocene, chromocene, ruthenocene, vanadocene and tungsteno-cene dihydride. The filling with metallocenes occurred from the vapor phase with formation of collinear metallocene chains inside the nanotubes [268], Also the filling with Zn diphenylporphyrin was successful and established from absorption spectra and Raman measurements [269]. 

These examples of functionalization of carbon nanotubes demonstrate that the chemistry of this new class of molecules represents a promising field within nanochemistry. Functionalization provides for the potential for the manipulation of their unique properties, which can be tuned and coupled with those of other classes of materials. The surface chemistry of SWCNTs allows for dispersibility, purification, solubilization, biocompatibility and separation of these nanostructures. Additionally, derivatization allows for site-selective nanochemistry applications such as self-assembly, shows potential as catalytic supports, biological transport vesicles, demonstrates novel charge-transfer properties and allows the construction of functional nanoarchitectures, nanocomposites and nanocircuits. 

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Stabilization of highly reactive species in molecular bowls and capsules with an endohedral functionality 97LA2393. 

Fig. 1.3 Functionalization pathways for SWNTs (a) defect-group functionalization, (b) covalent side-wall functionalization, (c) noncovalent exohedral functionalization with surfactants, (d) noncovalent exohedral functionalization with polymers, and (e) endohedral functionalization with, for example, C60. For methods (b)-(e), the tubes are drawn in idealized fashion, but defects are found in real situations. From [103] with kind permission of Wiley.

Tsuchiya T, Akasaka T, Nagase S (2010) New vistas in fullerene endohedrals functionalization with compounds from main group elements. Pure Appl Chem 82 505-521... 

Fig. 14.7. Endohedral functionalization of the inner surface of a wheel-shaped M0154 type nanocluster by cystine ligands (polyhedral representation, carboxylate group in ball-and-stick).

Intercalation Compounds and Endohedral Functionalization of Carbon Nanotubes... 

Besides the substances mentioned so far, functionalized fuUerenes like the simple Bingel adduct can be intercalated into nanotubes as well (Section 2.5.5.2). The formation of peapods has further been described for metallocenes (e.g., ferrocene), porphyrines (e.g., erbium phthalocyanine complex) and small fragments of nanotubes. The most important prerequisite for the feasibility of inclusion is always a suitable proportion of sizes of both the tube and the structure to be embedded. For example, this effect can be observed for the intercalation of different cobaltocene derivatives into SWNT. The endohedral functionalization only takes place at an internal diameter of 0.92nm or above (Figure 3.100). But there is also an upper limit to successful incorporation. When the diameter of the nanotube is too large, the embedded species can easily diffuse away again from the host. Only few molecules are consequently found inside such a wide tube. 

Goto, K. Okazaki. R. Molecular bowls and capsules with an endohedral functionality The stabilization of highly reactive species in their inner phase. Liebigs Ann./Recueil... 

Figure 12.2 Several possible functionalization with polymers, (c) defect-group mechanisms for CNTs. (a) endohedral functionalization, (d) covalent sidewall...

The other approach to supramolecular assembly of CNTs entails endohedral functionalization, where molecules interact noncovalently with the inside wall of the CNT (Figure 1). CNTs have been endohedrally functionalized by various materials including Ceo fullerenes, liquid lead, metal oxides, manganese, " and water. ... 

For modeling the isolated environments of enzymes, molecular systans with open cavities containing covalently embedded functionalities should be desirable. This overview describes the design and development of nanoscale molecular cavities for regulation of the reactivities of endohedral functional groups, especially for kinetic stabilization of highly reactive species with their intrinsic reactivities unaffected. 

The low reactivity of 16b toward the nucleophile can be explained by assuming that the intramolecular hydrogen bonding of the OH group reduces the electrophilic-ity of the selenium center of the SeOH functionality, although the steric congestion around the SeOH functionality may also be responsible. These results clearly demonstrate that the calix[6]arene macrocycle of each conformation provides a considerably different environment for the endohedral functionality, regulating its properties and reactivity. 

Tominaga M, Suzuki K, Murase T, Fujita M (2005) 24-Fold endohedral functionalization of a self-assembled M,2L24 coordination nanoball. J Am Chem Soc 127 11950-11951... 

Abstract The chemistry of fullerenes and carbon nanotubes have highly contributed to the progress in the fundamental and applies science of these nanomaterials over the last 15 years. This review focuses on the non-covalent chemistry of fullerenes and carbon nanotubes with nitrogen and/or oxygen containing heterocydic molecules such as porphyrin, DNA, protein, peptide and carbohydrate. Not only exohedral but also endohedral functionalization is reviewed, because the above guest molecules can interact with both faces of the carbon nanotubes. New terminology is also proposed in the structural and stereochemistry of carbon nanotubes. 

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