Peptide nanotubes from dipeptides

Figure 6 A (a) Schematic of the formation of tubular (single or multiwalled), spherical, or fihrillar structures via dipeptide self-assembly, (b) Proposed model for the formation of aligned peptide nanotube arrays. Scanning electron micrograph of (i) the vertically aligned peptide nanotubes, (ii) the nanotube arrays, and (iii) an individual nanotube obtained. Reprint with permission from Ref. [7].

Figure 19 Schematic representation of peptide nanotube formation from dipeptides and diketopiperazines.

The first dipeptide nanotube system was L-Val-L-Ala (VA), which forms crystals with narrow hydrophobic channels (diameter about 5 A) lined by peptide side chains.This structure is conceptually different from those of the cyclic peptides in that the pores are generated from self-assembly of small molecules, which are hydrogen bonded, head-to-tail, into helices (Fig. 3a). The extremely robust three-dimensional hydrogen-bonding scaffold was since observed for a series of other hydro-phobic dipeptides.Pore size can be regulated from 3.3 A (L-Ile-L-Val) to 5.2 A (L-Ala-L-Val) by adjusting the bulk of the hydrophobic side chains. Furthermore, L-Ala-L-Val has pores that can adapt their shapes and sizes to absorb large solvent molecules like 2-butanol. 

Peptide-based self-assembly is capable of synthesizing nanomaterials with various microstructures from tubes to spheres. Dipeptides, probably the simplest building blocks with a versatility in controlling microstructures, can form tubular, spherical, fibrous, or bundle, and array structures by modifying motifs on the dipeptides and/or altering synthesis conditions (Figure 6.4a). For example, the Alzheimer s p-amyloid peptide with diphenylalanine motif forms multiwaUed nanotubes when the peptide is... 

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