Helical nanotubes

Fig. 10. Growth mechanism proposed for the helical nanotubes (a) and helicity (b), and the model that gives the bridge and laminated tip structure (c).

Recently, a series of surfactant-like peptides were found to form helical nanotubes.112 The anionic peptide monomers were composed of a head group of one or two aspartic acids and a hydrophobic tail containing six residues... 

The self-assembling cyclic D,L-cc-peptide nanotubes described demonstrate high stability on surfaces even after two months exposure to ambient temperature. NDI peptide nanotubes 18 may provide a facile method for the preparation of a new class of synthetic biomaterials [16b, 34a]. Recently Sanders and co-workers demonstrated the formation of amino acid-derived NDI hydrogen-bonded supramo-lecular organic M-helical nanotubes in nonpolar solvents and also in the solid state [34b]. The hydrogen-bonded supramolecular nature of the helical nanotubes was confirmed by the circular dichroism (CD) spectrum in chloroform with the addition of methanol, destruction of the supramolecular nanotubes was observed, due to the capabilities of such an aprotic solvent to compete for hydrogen-bond interactions [34b]. 

Panto GD, Wietor J-L, Sanders JKM (2007) Filling helical nanotubes with C60. Angew Chem Int Ed 46 2238-2240... 

It was not long after the discovery of carbon nanotubes before specimens with coiled or helical shapes were observed. These helical nanotubes (hMWNT) are often found as by-product in the synthesis of multiwalled nanotubes, yet by now a directed preparation has succeeded as well. Their extraordinary shape turns the helical nanotubes into an interesting subject of research as the expected electronic properties like inductive effect under electrical current should enable an application, for example, as nanocoils. ... 

Figure 3.31 Helical nanotubes feature both five- and seven-membered rings (a) ( AlP 2002). There are spiral (b) ( ACS 2003) as well as twisted structures (c) ( APS 1993).

The production of hMWNT is possible on different ways. For instance, they are the main product of converting pyridine or toluene in a CVD apparatus in a stream of hydrogen at about 1100°C in the presence of iron pentacarbonyl. But also the reduction of diethyl ether at ca. 700 "C on zinc yields up to 80% of helical nanotubes. 

FIGURE 5.2.15 (a) The helical conformation of PHT molecules. Their one-dimensional aggregation into helical nanotubes side view (b) top view (c). (Kiriy, N. et al.. Nano. Lett., 3(6), 707, 2003. With permission.)... 

Fig. 6.12 Compound 12 and its progressive self-assembly into helical nanotubes using a combination of triple hydrogen bonding and ji-ti stacking. The arrow shows the starting point for tube formation...

In the next paragraph in the frame work of our shape analysis we shall smdy the minimum number of eigenvectors of the adjacency matrix and the Laplacinan in order to obtain proper drawing of nonspherical structures. Before the conclusion we present a method for drawing fullerenes, straight, toroidal and helical nanotubes, and nanotube junctions with the help of only three eigenvectors of a matrix. 

We tested our ideas for several structures. Here we present our results obtained for nanotube junctions nano tori and helical nanotubes. We calculated the interatomic interactions with the help of the Brenner potential (Brenner 1990) and harmonic potentials as well. In the Breimer potential there are first neighbour and second neighbour interactions. 

Figure 43 (Top) Schematic model of the helical nanoribbon, (a) Molecular structure and backbone of cholate illustrating the facial amphiphiUcity and molecular size (b) the molecular aggregate that is the minimum constitution unit of a bilayer type of cholate host framework (the blue dotted lines denoted H-bond) (c) scheme of twisted nanoribbon composed of parallel, longitudinal stripes and (d) top view and (e) cross-section view of the molecular model. (Bottom) (f and g) TEM and (h) SEM images of ZnS semiconductor helical nanotubes. (Reproduced with permission from Ref. 77. American Chemical Society, 2009.)...

Sanders et al. discovered a new class of helical nanotubes in nonpolar solution and in the soUd state from N,N -dimethylnaphthalenediimide (Figure 21b). These structures are easily prepared and they possess a uniform core that can potentially bind to a variety of guests through the side chains, which are derived from amino acid residues. It was observed that the chirality of the nanotubes is determined by the constituent anfino acid, but this is independent of the nature of the side chains. 

Figure 12.2 Schematic illustration of self-assembly process of RNTs. (a) Twin G C motifs with an RGDSK peptide (b) rosette-like supermacrocycle assembled from six motifs and (c) rosettes stacked up into stable helical nanotubes with an 11A hollow core, 3-4 nm in diamet and up to several pm long. Atomic force microscopy image of (d) twin DNA-based RNTs with RGDSK peptide, (e and f) twin DNA-based RNTs with an aminobutane linker (TBL).

Another family of organic molecules that spontaneously form helical nanotubes are the long hydrogen bonding-driven aiyl-based foldamers [17-19]. The main considerations for the structural design of helical foldamers are the size of the monomers and the substitution pattern of the aromatic rings used. Indeed, once... 

Fig. 8.2 Hydrogen bonded helical nanotubes from discrete aliphatic oligomers...

Sanders and coworkers have recently found supramolecular helical arrays of C o molecules in the tubular cavity of helical organic nanotubes composed of a-amino acid functionalized naphthalenediimides (10), which self-assembled to form hydrogen-bonded helical nanotubes in a nonpolar solution and in the solid state (Figure 6.11) [59]. The CD spectrum of the L-10-C,so complex exhibited weak but apparent Cotton effects at 595 and 663 nm due to electronic transitions of C o as... 

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