Nanotubes self-assembled

As an extension of Ghadiri s study, a 12-residue cyclic peptide, cyclo[(Gln-D-Ala-Glu-D-Ala),], afforded self-assembled nanotube materials having a uniform 13-A tailored pore diameter. Specifically sized tubular nanostructures with channel structures can expect various applications. ... 

A different kind of self-assembled nanotubes (Figure 4.12) are spontaneously built from cyclic peptides made up of alternating D- andL-amino acids. As predicted by DeSantis group in the mid 1970s [43], the octapeptide cyc/o-[-(D-Ala-Glu-Z)-Ala-Gln)2] 94 [44a] is approximately planar with NH and C=0 bonds orientated perpendicularly to the mean plane of the macro-ring thus... 

Figure 4.12, Self-assembled nanotube built from cyclic peptides.

Figure 14.16 (a) Structure of amphiphile 14.10 (b and c) SEM images of self-assembled nanotubes... 

Fig. 2 (a) Top view of the molecule I indicating H-bonding interactions observed in the self-assembled nanotube. The arrow indicates the direction of the nanotube assembly, (b) Schematic representation of the proposed non-classical H-bonding interactions between the NDIs units... 

Fig. 41 Schematic representation of the self-assembled nanotube and the competition experiment with Cg0 and ion pairs. Picture-, photographical comparison of a solution of 2 + C60 in the presence of different ion pairs [32]...

Khazanovich, N., Granja, J.R., McRee, D.E., Milligan, R.A., and Ghadiri, M.R. Nanoscale tubular ensembles with specified internal diameters. Design of a self-assembled nanotube with a 13 angstrom pore. J. Am. Chem. Soc. 116, 6011-6012, 1994. 

Channels in organic crystals are not uncommon. Evidently, such channels are genuine self-assembled nanotubes throughout the crystal in parallel well-ordered arrangement, the technical use of which awaits urgent exploration beyond solid-state chemistry. Channels in non-layered and often 3D-interlocked crystals are characteristically different from cleavage planes in layered structures, but there are... 

Figure 14.16 (a) Structure of amphiphile 14.10 (b and c) SEM images of self-assembled nanotubes of 14.10 under various conditions (scale bars 100 and 50 nm, respectively), (d) proposed mechanism for the assembly process (reproduced from [24] with permission from AAAS). 

Self-assembling nanotubes from cyclic peptides and depsipeptides ... 

Fig. 5 Examples of systems able to form channels in membranes. Left the Ghadiri s self-assembled nanotube formed by cyclopeptides. Right The Voyer s 21 amino acid peptide containing six 21-crown-7 L-phenylalanines. In a membrane, the peptide adopts an a-helical conformation that allows the partial alignment of the macrocycles, one over the other.

Self-Assembled Nanotubes and Nanocoils from TT-Conjugated Building Blocks... 

Before the conclusion of this section, it should be mentioned that the stability of the self-assembled nanotubes under limited conditions may restrict their apphcations. To overcome this, Meier and coworkers [ 17] as well as Win-nik. Manners, and coworkers [44] performed crosslinking reactions to their self-assembled nanotubes. The latter team then used their cross-linked nanotubes as template for the preparation of Ag nanoparticles encapsulated in solvent-dispersible nanotubes [49]. 

Block copolymer nanotubes can be prepared either directly from block copolymer self-assembly in block-selective solvents or from the chemical processing of ABC triblock copolymer nanofibers. There has been only one report on the formation of self-assembled nanotubes from coil-coil AB diblocks in block selective solvents, and it occurred for a sample with a very low weight fraction of the soluble block. Nanotubes were formed from coil-coil-coil ABA triblock copolymers at much higher weight fractions for the soluble A blocks. Still, lower soluble block weight fractions were required for nanotube than for vesicle formation. It remains to be seen if these trends can be generalized to other block copolymers containing purely coil blocks. 

The self-assembly of crystalline-coil and rod-coil diblock copolymers in block-selective solvents presented quite some surprises. Crystalline-coil diblocks formed tubular nanoaggregates in block-selective solvents for the coil blocks at coil to crystalUne block repeat unit number ratios substantially larger than 1, e.g., 12 and 18 for the PFS-PDMS diblock copolymers. This made the block copolymer nanotubes much easier to access. It again remains to seen if such a trend can be generalized to other diblock copolymers. Thus, much remains to be done to establish the best experimental conditions for formation of self-assembled nanotubes. Theories need to be developed to understand the formation and property of self-assembled block copolymer nanotubes. 

Programs for the preparation of self-assembling nanotubes have aimed at a variety of different structures (some inspired by nature), including helically folded linear molecules, hollow bundles of rod-like units, rolled-up sheets, helically juxtaposed truncated wedges, and stacked rings (Figure la-e, respectively). 

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