Aromaticity nanotube

In Fig. 1 is shown a HRTEM image of part of the end of a PCNT. The initial material consisted of carbon nanotubes upon which bi-conical spindle-like secondary growth had deposited[21], apparently by inhomogeneous deposition of aromatic carbonaceous, presumably disordered, layers on the primary substrate nanotube. Prior to further heat treatment, the second-... 

Fiber spinning, 11 174, 175, 170-171 carbon-nanotube, 13 385-386 methods of, 16 8 models of, 11 171-172 of polyester fibers, 20 12-15 Fiber structure, of aromatic polyamides, 19 727... 

Rajendra J, Baxendale M, Rap LGD, Rodger A (2004) Flow linear dichroism to probe binding of aromatic molecules and DNA to single-walled carbon nanotubes. J. Am. Chem. Soc. 126 11182-11188. 

The diameter of the nanotube is an additional important parameter, with smaller tubes presenting enhanced curvature and consequently enhanced reactivity. One last aspect affecting reactivity is the helicity of the carbon nanotubes. In metallic CNTs, the aromaticity is slightly lower than in the semiconducting types, rendering the former more susceptible to functionalization. 

As for the covalent type, modification of CNTs by this approach has as its first goal to lead to debundling of the tubes, thus increasing their solubility and facilitating their manipulation. However, while the covalent method destroys the extended aromatic framework, noncovalent interactions preserve the original regular carbon network. This is important in those applications requiring use of the nanotubes without alteration of their electronic and optical properties, a process that normally occurs when the aromatic periodicity is disrupted. 

Encapsulation of different entities inside the CNT channel stands alone as an alternative noncovalent functionalization approach. Many studies on the filling of carbon nanotubes with ions or molecules focus on how the presence of these fillers affects the physical properties of the tubes. From a different point of view, confinement of materials inside the cylindrical structure could be regarded as a way to protect such materials from the external environment, with the tubes acting as a nanoreactor or a nanotransporter. It is fascinating to envision specific reactions between molecules occurring inside the aromatic cylindrical framework, tailored by CNT characteristic parameters such as diameter, affinity towards specific molecules, etc. 

A. Ghosh, K.V. Rao, R. Voggu, S. J. George, Non-covalent functionalization, solubilization of graphene and single-walled carbon nanotubes with aromatic donor and acceptor molecules, Chemical Physics Letters, vol. 488, pp. 198-201, 2010. 

Nish, A. Hwang, J.-Y. Doig, J. Nicholas, R. J., highly selective dispersion of single-walled carbon nanotubes using aromatic polymers. Nat. Nano. 2007, 2, 640-646. 

Accordingly, many reactions can be performed on the sidewalls of the CNTs, such as halogenation, hydrogenation, radical, electrophilic and nucleophilic additions, and so on [25, 37, 39, 42-44]. Exhaustively explored examples are the nitrene cycloaddition, the 1,3-dipolar cycloaddition reaction (with azomethinylides), radical additions using diazonium salts or radical addition of aromatic/phenyl primary amines. The aryl diazonium reduction can be performed by electrochemical means by forming a phenyl radical (by the extrusion of N2) that couples to a double bond [44]. Similarly, electrochemical oxidation of aromatic or aliphatic primary amines yields an amine radical that can be added to the double bond on the carbon surface. The direct covalent attachment of functional moieties to the sidewalls strongly enhances the solubility of the nanotubes in solvents and can also be tailored for different... 

Fig. 4.12 The structural relationship between graphene sheet and single-walled carbon nanotube arrows point to two alternative directions of rolling circles inside rings reflect on aromatic character of carbon rings and delocalization of resonant electrons inside them...

About 98% of the fibers employed in composites are glass (Sections 12.5 and 12.6), carbon (graphite, carbon fibers, etc. Section 12.16), and aromatic nylons (often referred to as aramids Section 4.8). New composites are emerging that employ carbon nanotubes and the fibers (Section 12.17). Asbestos (Section 12.13), a major fiber choice years ago, holds less than l%i of the market today because of medical concerns linked to it. 

Title Copolymerization and Copolymers of Aromatic Polymers with Carbon Nanotubes and Products Made Therefrom... 

Tour et al. (3) dispersed single-walled nanotubes in water by functionalizing with aromatic sulfonates. 

The present review will be based on the classical views of aromaticity [14-16], confining it to two dimensions, although it has been customary to ascribe the exceptional stability of icosahedral closo-carboranes to their three-dimensional aromaticity [17, 18], The discovery of fullerenes, nanocones, and nanotubes has opened new vistas for bent and battered benzene rings. Also, it is possible to obtain benzenic rings... 

Noncovalent approaches can usually preserve the structures and properties of carbon nanotubes after functionalization17 (though not necessarily the near-infrared absorption characteristics due to well-established doping effects), thus are equally important to the biocompatibilization and bioapplications of nanotubes.15 Among commonly employed noncovalent schemes are surfactant dispersion,18 tt-tt stacking with aromatic compounds,19 and polymer wrapping.20... 

The past decade has led to the detection of new carbon allotropes such as fullerenes26 and carbon nanotubes,27 28 in which the presence of five-mem-bered rings allows planar polycyclic aromatic hydrocarbons to fold into bent structures. One notes at the same time that these structures are not objects of controlled chemical synthesis but result from unse-lective physical processes such as laser ablation or discharge in a light arc.29 It should be noted, on the other hand, that, e.g., pyrolytic graphitization processes, incomplete combustion of hydrocarbon precursors yielding carbon black, and carbon fibers30 are all related to mechanisms of benzene formation and fusion to polycyclic aromatic hydrocarbons. 

The diphenylalanine nanotube sensors were based on the observation that peptide nanotubes improve the electrochemical properties of graphite and gold electrodes when deposited directly onto the electrode surface (Yemini et al., 2005b). The high surface area of the nanotubes and the potential alignment of aromatic residues are thought to contribute to the observed increase in conductivity. This property makes nanotube-coated electrodes and hydrophobin-coated electrodes suitable for use as amperometric biosensors that produce a current in response to an electrical potential across two electrodes. 

Other research has focused on the interaction of cells with peptide structures that assemble via aromatic interactions. Cells have been grown on the surface of gels formed by Fluorenylmethoxycarbonyl (FMOC) modified diphenylalanine nanotubes (Mahler et al., 2006). Although cells were only grown for short time frames (24 h), the cells were viable on these scaffolds. 

Such a molecule can be stabilized by a system of delocalized Ji-electrons, which is closed into a toroid of 10 aromatic rings. Reactive sites are four CH groups, which are at the ends of this molecular tube. Such substances belong apparently to a new class of organic compounds, which is intermediate between planar polycyclic aromatic hydrocarbons and three-dimensional fullerenes, nanotubes. Quantum-chemical calculations of the electronic and spatial structure of C32H8 and some other molecules indicate that they have an increased reactivity and semiconductor properties. 

---